Tuesday 27 December 2011
Sunday 18 December 2011
Hydraulic Safety
Hydraulic Safety
Anyone involved with Hydraulic equipment can be subjected to considerable risk unless good working practice is always adopted. Hydraulic machines are often very powerful with large dynamic forces and high pressure fluid that can also sometimes be scalding hot.
When working on hydraulic equipment it is a good idea to do an assessment of risk (download example from www.hydraulicbrain.com)
Never work on systems until you are sure that the pump is switched off and all suspended loads are lowered so nothing can fall or move should you remove pipe-work.Accumulators are a source of large potential energy so ensure they are completely discharged.
Prevent equipment being started up by third parties. Maybe you can lock the system,remove the key,electricalfuses and put up signs to say that the system is being worked on and must not be used
There are many dangers for the Engineer and many things that you can do to make yourself safe.
For more stuff on Hydraulic Safety log on to www.hydraulicbrain.com
Very best
Bob
Anyone involved with Hydraulic equipment can be subjected to considerable risk unless good working practice is always adopted. Hydraulic machines are often very powerful with large dynamic forces and high pressure fluid that can also sometimes be scalding hot.
When working on hydraulic equipment it is a good idea to do an assessment of risk (download example from www.hydraulicbrain.com)
Never work on systems until you are sure that the pump is switched off and all suspended loads are lowered so nothing can fall or move should you remove pipe-work.Accumulators are a source of large potential energy so ensure they are completely discharged.
Prevent equipment being started up by third parties. Maybe you can lock the system,remove the key,electricalfuses and put up signs to say that the system is being worked on and must not be used
There are many dangers for the Engineer and many things that you can do to make yourself safe.
For more stuff on Hydraulic Safety log on to www.hydraulicbrain.com
Very best
Bob
Sunday 6 November 2011
The Counterbalance valve
The counterbalance valve is used for load holding and prevents the load running away uncontrolled. The valve automatically throttles the outgoing flow using a pilot signal from the input flow leg to the ram or motor. The valve symbol is very similar to the Relief valve with a normally closed function and a check valve looped around the main valve.
To open the valve it will need a pilot pressure and for very large loads this should be as small as possible where lighter loads should be higher. The valve will be made with a designed pilot ratio, this is ratio of the pilot pressure against the induced load pressure to open the valve and can be typically 3:1 to 10:1
To establish the way to set up the Counterbalance valve you must know the Pilot Ratio. Pilot Pressure= Valve Setting Pressure – Pressure induced by load divided by the Pressure Ratio + the ratio of piston area divided by the annular ram . A hydraulic motor would be 1.
If we are using a hydraulic motor on a winch it will be important to ensure that there is enough pressure to release the brake. This might require a low Pressure Ratio to achieve enough pressure to release the brake.
If you do not set these valves up correctly the system can become unstable, the ram or motor may not move and in the case of winches the brake might not release.
For more about load holding become a member of www.hydraulicbrain.com
Very best wishes
Bob
To open the valve it will need a pilot pressure and for very large loads this should be as small as possible where lighter loads should be higher. The valve will be made with a designed pilot ratio, this is ratio of the pilot pressure against the induced load pressure to open the valve and can be typically 3:1 to 10:1
To establish the way to set up the Counterbalance valve you must know the Pilot Ratio. Pilot Pressure= Valve Setting Pressure – Pressure induced by load divided by the Pressure Ratio + the ratio of piston area divided by the annular ram . A hydraulic motor would be 1.
If we are using a hydraulic motor on a winch it will be important to ensure that there is enough pressure to release the brake. This might require a low Pressure Ratio to achieve enough pressure to release the brake.
If you do not set these valves up correctly the system can become unstable, the ram or motor may not move and in the case of winches the brake might not release.
For more about load holding become a member of www.hydraulicbrain.com
Very best wishes
Bob
Saturday 29 October 2011
What is maximum pressure?
These days we expect hydraulic pumps should be fully supported with detailed technical information ensuring that we use the pump in the correct application.
Often we have pages of stuff showing everything from displacement to recommended oil type.
I often find that the pressure duty is not well defined like what pressure can I safely generate without the pump falling apart. You will read descriptions like continuous, intermittent and peak.
Continuous speaks for itself but what about intermittent and peak, what does this description really mean.
Many years ago when I sold hydraulic components for a well known manufacturer the pumps had different ratings for industrial than mobile. For what I can only imagine were commercial reasons, the mobile pump pressures were much higher.
I have also used some pumps well outside their recommended pressure ranges (only for specific applications) and although not a practice I recommend I do wonder what technical basis manufacturers use to determine their pump pressure ratings.
I would like to see a graph with a direct correlation between pressure and life. I want to know that if I design a system that runs once a month for 15minutes at higher than normal pressure should I need to spend much more money on a more expensive pump.
Surely we should be able to get a better idea of pump life without always having to buy the highest spec pump or face the possibility of a bucket of scrap metal after just a few cycles.
Very best
Bob
Often we have pages of stuff showing everything from displacement to recommended oil type.
I often find that the pressure duty is not well defined like what pressure can I safely generate without the pump falling apart. You will read descriptions like continuous, intermittent and peak.
Continuous speaks for itself but what about intermittent and peak, what does this description really mean.
Many years ago when I sold hydraulic components for a well known manufacturer the pumps had different ratings for industrial than mobile. For what I can only imagine were commercial reasons, the mobile pump pressures were much higher.
I have also used some pumps well outside their recommended pressure ranges (only for specific applications) and although not a practice I recommend I do wonder what technical basis manufacturers use to determine their pump pressure ratings.
I would like to see a graph with a direct correlation between pressure and life. I want to know that if I design a system that runs once a month for 15minutes at higher than normal pressure should I need to spend much more money on a more expensive pump.
Surely we should be able to get a better idea of pump life without always having to buy the highest spec pump or face the possibility of a bucket of scrap metal after just a few cycles.
Very best
Bob
Sunday 16 October 2011
Mystery Hydraulic Fault
Only a few days ago I had a call to look at a problem on a log handling system in a Saw Mills.
I was shown a fault on a log flipper. Flippers that can turn the log to any position to pass through the saw. Each pair of flipper rams are connected to a 3 position CETOP 5 solenoid valve mounted on a common manifold. An unloading valve is electrically sequenced to prevent the pump being continuously on load and creating heat.
So now for the problem, if a set of flippers were moved to say, half way and stopped and the other set of flippers were switched to move, the first set would continue moving. Now I hear you say, what ghost like things are going on in them there Hydraulics.
I got down close to the manifold and soon identified the valve responsible for the first set of flippers and removed the Electrical Hirschman plugs to see if I could repeat the problem with the electrics removed. Low and behold I could!
I would have bet a weeks pay that this was an electrical problem and be able to pass over to the Electrician. Now was the time to look very closely and find out what was going on as this was becoming a much more interesting fault.
“Ah! Found it,” I said.
The symbol on the valve showed that it was “Detented” making it not a 3 position valve but 2 position.
A detent will allow the solenoid to fire the spool across from one position to the other and hold the spool in that position even when the electrical signal is removed. So with our flipper when the ram is moved half way and the signal is removed and the dump valve diverts the flow to tank the ram will stop moving but only until the dump valve is re energised and allow the ram to complete its movement. So by operating the other flippers the first set will continue to move.
So how did a 2 position detent valve end up on this manifold block doing this job and causing this problem? Seems that no one knows except ghosties and things that go bump in the night.
Advice for you budding Hydraulic fault finders. Sometimes you will come across faults that will remain a mystery and no one will admit to touching.
More Hydraulics at www.hydraulicbrain.com
Cheers
Bob
I was shown a fault on a log flipper. Flippers that can turn the log to any position to pass through the saw. Each pair of flipper rams are connected to a 3 position CETOP 5 solenoid valve mounted on a common manifold. An unloading valve is electrically sequenced to prevent the pump being continuously on load and creating heat.
So now for the problem, if a set of flippers were moved to say, half way and stopped and the other set of flippers were switched to move, the first set would continue moving. Now I hear you say, what ghost like things are going on in them there Hydraulics.
I got down close to the manifold and soon identified the valve responsible for the first set of flippers and removed the Electrical Hirschman plugs to see if I could repeat the problem with the electrics removed. Low and behold I could!
I would have bet a weeks pay that this was an electrical problem and be able to pass over to the Electrician. Now was the time to look very closely and find out what was going on as this was becoming a much more interesting fault.
“Ah! Found it,” I said.
The symbol on the valve showed that it was “Detented” making it not a 3 position valve but 2 position.
A detent will allow the solenoid to fire the spool across from one position to the other and hold the spool in that position even when the electrical signal is removed. So with our flipper when the ram is moved half way and the signal is removed and the dump valve diverts the flow to tank the ram will stop moving but only until the dump valve is re energised and allow the ram to complete its movement. So by operating the other flippers the first set will continue to move.
So how did a 2 position detent valve end up on this manifold block doing this job and causing this problem? Seems that no one knows except ghosties and things that go bump in the night.
Advice for you budding Hydraulic fault finders. Sometimes you will come across faults that will remain a mystery and no one will admit to touching.
More Hydraulics at www.hydraulicbrain.com
Cheers
Bob
Saturday 8 October 2011
Engineering v IT
Having spent over 45 years in Engineering I now have ways of doing things that has become second nature and one of the basic rules Engineers work by is clarity.
Everything from drawings, instructions or systems must be unambiguous and crystal clear. The consequences of unclear instructions can be disastrous.
IT on the other hand comes from a very different world. Trying to follow instructions on how to set up a program or install some piece of equipment is rarely clear.
A typical example of my point happened a few days ago when I tried to install a new Broadband Router. No instruction except a brief letter giving me a user name, password and WEP Key code.
Need I say that I could not install the system? I contacted the helpline and they gave me a new User name and Password that differed from that sent to me in their letter. When I pointed out that the details did not match my letter I was told that there are about six user names and passwords for various parts of the system. The password I needed was in fact a Serial Number on the machine. In Engineering if it was gave something a Password it would remain so and not suddenly turn into a Serial Number. We have terminology that does not changed and names that are clear and unambiguous.
Until IT people get more discipline,consistency and accuracy in how they describe things and clearer instructions they give out we will continue to get it wrong, get frustrated and cost us all more time and money.
Cheers
Bob
Everything from drawings, instructions or systems must be unambiguous and crystal clear. The consequences of unclear instructions can be disastrous.
IT on the other hand comes from a very different world. Trying to follow instructions on how to set up a program or install some piece of equipment is rarely clear.
A typical example of my point happened a few days ago when I tried to install a new Broadband Router. No instruction except a brief letter giving me a user name, password and WEP Key code.
Need I say that I could not install the system? I contacted the helpline and they gave me a new User name and Password that differed from that sent to me in their letter. When I pointed out that the details did not match my letter I was told that there are about six user names and passwords for various parts of the system. The password I needed was in fact a Serial Number on the machine. In Engineering if it was gave something a Password it would remain so and not suddenly turn into a Serial Number. We have terminology that does not changed and names that are clear and unambiguous.
Until IT people get more discipline,consistency and accuracy in how they describe things and clearer instructions they give out we will continue to get it wrong, get frustrated and cost us all more time and money.
Cheers
Bob
The Benefits of Hydraulics
With rapid developments in Electric motor drives and the reduction in costs you might wonder if hydraulics is relegated to past technology.
There can be no doubt that electric drives have replaced some hydraulic applications, especially in the machine tool industry. Electric drives are cleaner, more efficient provide better control but hydraulics can still provide a better and often the only solution for many applications. Hydraulics provides better power to weight ratio. You can get a lot of power out of a very small package and where size and weight is important it will be the best choice. For small forces, the electric motor and worm drive can be a “no brainer” but if large forces are required for applications like Earth moving equipment, presses, jacks etc Hydraulics (at the moment) have no better alternatives.
Hydraulics provides other benefits that include:
1) Easy direction control
2) Easy speed control
3) Easy force control
4) Can take shock
5) Linear and rotary drives from the same system
6) No lubrication required
7) You can stall the drive without damage
8) Easy to keep cool
If you specialise in Hydraulic, pneumatic or electrical drive systems always try to use the best solution for the application and not just because you have a personal bias to a particular technology.
Very best Bob
www.hydraulicbrain.com
There can be no doubt that electric drives have replaced some hydraulic applications, especially in the machine tool industry. Electric drives are cleaner, more efficient provide better control but hydraulics can still provide a better and often the only solution for many applications. Hydraulics provides better power to weight ratio. You can get a lot of power out of a very small package and where size and weight is important it will be the best choice. For small forces, the electric motor and worm drive can be a “no brainer” but if large forces are required for applications like Earth moving equipment, presses, jacks etc Hydraulics (at the moment) have no better alternatives.
Hydraulics provides other benefits that include:
1) Easy direction control
2) Easy speed control
3) Easy force control
4) Can take shock
5) Linear and rotary drives from the same system
6) No lubrication required
7) You can stall the drive without damage
8) Easy to keep cool
If you specialise in Hydraulic, pneumatic or electrical drive systems always try to use the best solution for the application and not just because you have a personal bias to a particular technology.
Very best Bob
www.hydraulicbrain.com
Sunday 2 October 2011
Hydraulic Winches
Hydraulic Winches
My most common fear about Winches and Cranes is that they can both cause serious accidents if used or designed incorrectly.
Most of the winches I am involved with are on boats and range from small 1-2 tons pull to many tens of tons. The basic design is a drum with a coil of wire rope. This is driven by a hydraulic motor through a gearbox. The controls can just a very simple hand valve or much more complex with joystick and servo valve that can provide steady pull or payout speeds.
Read in full at www.hydraulicbrain.com
Bob Jackson
www.hydraulicbrain.com
Please revisit Hydraulic Brain and learn more about the fascinating subject of Hydraulics.
My most common fear about Winches and Cranes is that they can both cause serious accidents if used or designed incorrectly.
Most of the winches I am involved with are on boats and range from small 1-2 tons pull to many tens of tons. The basic design is a drum with a coil of wire rope. This is driven by a hydraulic motor through a gearbox. The controls can just a very simple hand valve or much more complex with joystick and servo valve that can provide steady pull or payout speeds.
Read in full at www.hydraulicbrain.com
Bob Jackson
www.hydraulicbrain.com
Please revisit Hydraulic Brain and learn more about the fascinating subject of Hydraulics.
Saturday 24 September 2011
Dangerous Cranes
I think most will agree that hydraulic crane safety should be of paramount importance and I would like to mention just a few observations about the use of this potentially dangerous piece of machinery.
In my opinion the safest type of crane has been designed to prevent overloading. Not just on the main lift but more importantly where you pick up a load and then telescope out. As the telescope extends increasing its length the main lift cylinder pressure also increases in proportion.
Now some cranes have load sensing devices that will disengage the telescope so that overloading cannot occur and stop the telescope extending when the maximum load is exceeded.
Also the counterbalance valve can also relieve and lower the load in a controlled way.
However there are some cranes that I have come across where they have been fitted with a simple hand valve with all blocked centre ports. These cranes have often been salvaged and the hydraulics replaced by people not proficient in hydraulic systems or crane design. Unwittingly the users of these cranes are just waiting for disaster to strike, at best causing costly damage and at worst serious injury.
See more on www.hydraulicbrain.com
very best
Bob
In my opinion the safest type of crane has been designed to prevent overloading. Not just on the main lift but more importantly where you pick up a load and then telescope out. As the telescope extends increasing its length the main lift cylinder pressure also increases in proportion.
Now some cranes have load sensing devices that will disengage the telescope so that overloading cannot occur and stop the telescope extending when the maximum load is exceeded.
Also the counterbalance valve can also relieve and lower the load in a controlled way.
However there are some cranes that I have come across where they have been fitted with a simple hand valve with all blocked centre ports. These cranes have often been salvaged and the hydraulics replaced by people not proficient in hydraulic systems or crane design. Unwittingly the users of these cranes are just waiting for disaster to strike, at best causing costly damage and at worst serious injury.
See more on www.hydraulicbrain.com
very best
Bob
Sunday 18 September 2011
My Trip to Breast
The use of hydraulics is often simply down to the ingenuity of the designer.
I have just returned from France after commissioning a hydraulic system on an Open 60 racing yacht, not the most likely place you would expect to find large hydraulic rams.
Designed and built by Target Fluid Services two 100mm bore rams are connected together in a push pull arrangement moving a 3ton keel from side to side. The canting keel ensures the boat is kept upright in an optimum position for maximum speed.
The most challenging part of the design is providing the lightest system possible but strong enough to take the large dynamic loads experienced in the worlds heaviest seas.
The boat has been sponsored by a Spanish company called Acciona who specialise in renewable energy. The boat is also eco friendly with many innovations to generate green power (as well as the sail). The boat is covered with solar cells and a Hydrogen cell system to generate electricity. This power is used to drive an electric motor for emergency use and for moving in and out of the harbour.
I apologise that we cannot show the hydraulic stuff inside the boat as the client is sensitive to showing this at present time but you can see the keel when a 90 degree test is being carried out and witnessed by IMOCA who are adjudicators for this class of boat.
Anyone who is keen on sailing I would suggest that you watch out for this boat when it starts on the racing circuit as I believe that it could be a very fast contender.
Very best
Bob
www.hydraulicbrain.com
Have you signed up yet for more information on Hydraulic Brain. It is great value and you get loads of hydraulic information. You can even advertise if you are looking for a job by sending us your details and we put it up on the site.
I have just returned from France after commissioning a hydraulic system on an Open 60 racing yacht, not the most likely place you would expect to find large hydraulic rams.
Designed and built by Target Fluid Services two 100mm bore rams are connected together in a push pull arrangement moving a 3ton keel from side to side. The canting keel ensures the boat is kept upright in an optimum position for maximum speed.
The most challenging part of the design is providing the lightest system possible but strong enough to take the large dynamic loads experienced in the worlds heaviest seas.
The boat has been sponsored by a Spanish company called Acciona who specialise in renewable energy. The boat is also eco friendly with many innovations to generate green power (as well as the sail). The boat is covered with solar cells and a Hydrogen cell system to generate electricity. This power is used to drive an electric motor for emergency use and for moving in and out of the harbour.
I apologise that we cannot show the hydraulic stuff inside the boat as the client is sensitive to showing this at present time but you can see the keel when a 90 degree test is being carried out and witnessed by IMOCA who are adjudicators for this class of boat.
Anyone who is keen on sailing I would suggest that you watch out for this boat when it starts on the racing circuit as I believe that it could be a very fast contender.
Very best
Bob
www.hydraulicbrain.com
Have you signed up yet for more information on Hydraulic Brain. It is great value and you get loads of hydraulic information. You can even advertise if you are looking for a job by sending us your details and we put it up on the site.
Saturday 17 September 2011
A New Racing Yacht
A New Racing Yacht
The Open 60 Racing enthusiasts will soon see a new radically designed boat entering this high performance class of Monohulls.
The Spanish boat Acciona has numerous cutting edge features including eco friendly power generating systems.
The canting keel hydraulic system was designed and supplied by Target Fluid Services Ltd, Southampton www.targetfluid.co.uk The right balance between lightness and strength was the greatest challenge and achieved using high grade Aerospace titanium alloy, designed using Solid Works and ANSI stress analysis software.
The hydraulics has many safety features and feedback systems that will provide valuable data for future optimisation.
Target Fluid Services and Hydraulic Brain wish the Team a safe and successful campaign.
More information contact target.fluid@btinternet.com
www.hydraulicbrain.com
The Open 60 Racing enthusiasts will soon see a new radically designed boat entering this high performance class of Monohulls.
The Spanish boat Acciona has numerous cutting edge features including eco friendly power generating systems.
The canting keel hydraulic system was designed and supplied by Target Fluid Services Ltd, Southampton www.targetfluid.co.uk The right balance between lightness and strength was the greatest challenge and achieved using high grade Aerospace titanium alloy, designed using Solid Works and ANSI stress analysis software.
The hydraulics has many safety features and feedback systems that will provide valuable data for future optimisation.
Target Fluid Services and Hydraulic Brain wish the Team a safe and successful campaign.
More information contact target.fluid@btinternet.com
www.hydraulicbrain.com
Saturday 10 September 2011
Problem at Sawmills
Whenever my home phone rings in the early hours of the morning it usually means one thing, trouble!
It was a call from the Sawmills. There pump and servo valve had gone down.
The system drives a carriage complete with log attached, back and forth through a huge band saw. Without the pump and servo the plant comes to a standstill.
The piston pump with servo valve is part of a closed circuit and coupled to a fixed displacement piston motor.
My customer had already decided to replace the hydraulic drive with an electric motor and inverter but delivery one still some weeks away. So was there anything we could do meantime?
Repair was out of the question, the pump was obsolete and repair would take weeks.
I decided to use an 11kw power-pack in storage and couple the motor open circuit. We installed a simple hand valve for the operator and by lunchtime the next day they were cutting wood.
I hope that if they have future problems with the inverter drive they will be able to get the same response?
Very Best
Bob
Find more on
www.hydraulicbrain.com
It was a call from the Sawmills. There pump and servo valve had gone down.
The system drives a carriage complete with log attached, back and forth through a huge band saw. Without the pump and servo the plant comes to a standstill.
The piston pump with servo valve is part of a closed circuit and coupled to a fixed displacement piston motor.
My customer had already decided to replace the hydraulic drive with an electric motor and inverter but delivery one still some weeks away. So was there anything we could do meantime?
Repair was out of the question, the pump was obsolete and repair would take weeks.
I decided to use an 11kw power-pack in storage and couple the motor open circuit. We installed a simple hand valve for the operator and by lunchtime the next day they were cutting wood.
I hope that if they have future problems with the inverter drive they will be able to get the same response?
Very Best
Bob
Find more on
www.hydraulicbrain.com
Monday 29 August 2011
Terminally sick systems
Over the years I have been called out to resolve a variety of hydraulic problems but there are some I call the terminally sick system or TSS for short. These are the systems that have gone unnoticed and uncared for that suddenly become mad, panic important because after the many years of abuse and unnoticed service they have finally decided to stop working.
The outside condition will often give the first clue to a TSS. It will be covered in a mixture of blackened oily deposits that has solidified over the years resembling greasy mud. When you look into the tank you recoil from the rancid smell of burnt oil and the colour has no resemblance to the once golden honey colour that was poured in from a new can. On taking a small sample of this gloop you hold it to the light and see a myriad of sparkling metallic particles and now you are convinced that you are dealing with a terminally sick system.
The customer is in panic because he cannot operate his machine and he will have to send everyone home if he can’t get it running within 24 hours and he has called you out because you are the expert and wants it fixed within the next few hours.
Yes, I have made up this story but it is not untypical of the type of breakdowns we are sometimes called out to resolve.
I have my own way of dealing with the TSS but I am more interested in how you would deal with this hydraulic emergency.
Very best
Bob
More stuff on www.hydraulicbrain.com
The outside condition will often give the first clue to a TSS. It will be covered in a mixture of blackened oily deposits that has solidified over the years resembling greasy mud. When you look into the tank you recoil from the rancid smell of burnt oil and the colour has no resemblance to the once golden honey colour that was poured in from a new can. On taking a small sample of this gloop you hold it to the light and see a myriad of sparkling metallic particles and now you are convinced that you are dealing with a terminally sick system.
The customer is in panic because he cannot operate his machine and he will have to send everyone home if he can’t get it running within 24 hours and he has called you out because you are the expert and wants it fixed within the next few hours.
Yes, I have made up this story but it is not untypical of the type of breakdowns we are sometimes called out to resolve.
I have my own way of dealing with the TSS but I am more interested in how you would deal with this hydraulic emergency.
Very best
Bob
More stuff on www.hydraulicbrain.com
Saturday 27 August 2011
Have hydraulic manufacturers become too arrogant?
I am sure that most of you will agree that getting new business and maintaining the existing is something that requires continued hard work. Most of the smaller businesses pay particular attention to giving good services and value their customers. I wish however I could say the same for the large manufacturers of hydraulic equipment. I am not sure if it would be a good idea to name and shame these companies but I guess that you might have a good idea of the ones I refer to.
I have some customers who buy branded products from me rather than deal direct. Not because I can save them money, in fact it’s likely it cost them more. It’s because they do not like dealing with the arrogant attitude so often associated with buying the parts they want. Comments like “You want it now, you must be joking, well if you don’t like 21 weeks delivery you can always go somewhere else!”
I notice that some of these companies do not even want to speak to us anymore. They hide behind a website with no means of contact other than an email address that they never reply to and finding a telephone number can take endless searching. I have been told by distributers that they also find it very difficult.
I rang a top brand servo manufacture for the name of someone who I could contact; I was told that the companies' policy was not to give out any names and that if I wanted I could send an email. The next time their rep knocks on my door or rings me up for an appointment you can guess what I will say to them!
We spend a great deal of time, effort and money trying to create a great experience for our customers as I am sure you guys do. We want our businesses to grow and be successful but some of these big companies have lost their desire or ability to give good service. Unfortunately for us we often have no choice but to continue to buy from them.
If you have had any experiences like me or disagree with my analysis I would love to hear from you.
Cheers
Bob
www.hydraulicbrain.com
I have some customers who buy branded products from me rather than deal direct. Not because I can save them money, in fact it’s likely it cost them more. It’s because they do not like dealing with the arrogant attitude so often associated with buying the parts they want. Comments like “You want it now, you must be joking, well if you don’t like 21 weeks delivery you can always go somewhere else!”
I notice that some of these companies do not even want to speak to us anymore. They hide behind a website with no means of contact other than an email address that they never reply to and finding a telephone number can take endless searching. I have been told by distributers that they also find it very difficult.
I rang a top brand servo manufacture for the name of someone who I could contact; I was told that the companies' policy was not to give out any names and that if I wanted I could send an email. The next time their rep knocks on my door or rings me up for an appointment you can guess what I will say to them!
We spend a great deal of time, effort and money trying to create a great experience for our customers as I am sure you guys do. We want our businesses to grow and be successful but some of these big companies have lost their desire or ability to give good service. Unfortunately for us we often have no choice but to continue to buy from them.
If you have had any experiences like me or disagree with my analysis I would love to hear from you.
Cheers
Bob
www.hydraulicbrain.com
Saturday 20 August 2011
Piston Rods
The piston rod is the key component to any hydraulic ram and probably the most prone to damage.
The rod must be the right length and diameter to avoid buckling and strong enough to take the load.
What I wish to focus on is the surface finish.
Many rods are made from high grade carbon steel and flash chromed. Often you can buy the material straight off the shelf and ready to machine the ends.
The chrome is used for its hardness and wear ability. Under the microscope it will appear like a crazed plate and if subject to a prolonged wet environment the chrome will soon show signs of rust and bubbling up of the plated surface.
On marine applications I once used stainless steel with chrome on top. The stainless was soft but corrosion resistant while the chrome is hard and porous. A great combination you might think. After a few months we discovered tiny marks in the chrome. Under a glass it appeared like a small crater with a very sharp edge.
The chrome was being pulled from the rod and we put this down to the electrolytic action of the seawater. We installed a sacrificial anode with little improvement. Eventually we replaced the rods with plain stainless steel. We suffer a little extra wear but keep the seals in good order.
Also do not make your rods with a too perfect finish. High polished rods will wear the seals due to reduced lubrication.
There are lots of other interesting things about piston rods but I just thought of a couple but please tell us about your experiences.
Cheers
Bob
Read more on www.hydraulicbrain.com
The rod must be the right length and diameter to avoid buckling and strong enough to take the load.
What I wish to focus on is the surface finish.
Many rods are made from high grade carbon steel and flash chromed. Often you can buy the material straight off the shelf and ready to machine the ends.
The chrome is used for its hardness and wear ability. Under the microscope it will appear like a crazed plate and if subject to a prolonged wet environment the chrome will soon show signs of rust and bubbling up of the plated surface.
On marine applications I once used stainless steel with chrome on top. The stainless was soft but corrosion resistant while the chrome is hard and porous. A great combination you might think. After a few months we discovered tiny marks in the chrome. Under a glass it appeared like a small crater with a very sharp edge.
The chrome was being pulled from the rod and we put this down to the electrolytic action of the seawater. We installed a sacrificial anode with little improvement. Eventually we replaced the rods with plain stainless steel. We suffer a little extra wear but keep the seals in good order.
Also do not make your rods with a too perfect finish. High polished rods will wear the seals due to reduced lubrication.
There are lots of other interesting things about piston rods but I just thought of a couple but please tell us about your experiences.
Cheers
Bob
Read more on www.hydraulicbrain.com
Sunday 14 August 2011
Grooves in Pistons
I was recommended a book “Hydraulic Control Systems” by Herbert E Merritt. Although the maths flies gently over my head there is some very interesting stuff for the Hydraulic enthusiast.
I recently asked a question about grooves in pump pistons and valve spools and what was their purpose. I found the answer and I will try to explain in my own Layman’s language.
With close tolerance pistons it is possible for hydraulic forces to create lateral movement on the piston forcing it to one side of the bore. This can cause stiction (hydraulic lock), extra leakage and a trap for contamination.
Just one groove on the piston can reduce the lateral forces by up to 40%. The grooves create a centreing effect and help prevent metal to metal contact between piston and bore. Adding more grooves will also be beneficial.
The depth and the width of the groove should be 10 times the clearance and the sides of the groove should be perpendicular to the bore.
Ref from Hydraulic Control Systems
More stuff on www.hydraulicbrain.com
I recently asked a question about grooves in pump pistons and valve spools and what was their purpose. I found the answer and I will try to explain in my own Layman’s language.
With close tolerance pistons it is possible for hydraulic forces to create lateral movement on the piston forcing it to one side of the bore. This can cause stiction (hydraulic lock), extra leakage and a trap for contamination.
Just one groove on the piston can reduce the lateral forces by up to 40%. The grooves create a centreing effect and help prevent metal to metal contact between piston and bore. Adding more grooves will also be beneficial.
The depth and the width of the groove should be 10 times the clearance and the sides of the groove should be perpendicular to the bore.
Ref from Hydraulic Control Systems
More stuff on www.hydraulicbrain.com
Saturday 13 August 2011
Things you remember
Anyone with a long career in hydraulics, I am sure will remember those times when things went badly wrong and ended with a few sleepless nights. The one etched in my distant memory was an application for a hydraulic riveting system. The client need several pressures all quite set close to each other. On the face of it a very simple straightforward project. We tested the system in the workshop and all seemed well before delivering it to the customers factory.
Within a few days we had the first of many phone calls.
It seemed that without warning the system started screaming so loud that the workers had to cover their ears.
By the end of the week the power pack was back. We tried all sorts of things to resolve the problem and each thing we tried we thought it was fixed, only to discover that within a few days it would start playing up again with the ear shattering noise.
In the end we admitted defeat and re reimbursed the client in full.
For me, at the beginning of my hydraulic career it was a huge blow and I considered that maybe I was not cut out for a future in hydraulics.
But you eventually move on and get bad experiences behind you with more successful jobs. However when I come across an application with two Relief valves in the same circuit I feel that familiar sickness again envelope my being.
Regards
Bob
more on www.hydraulicbrain.com
Within a few days we had the first of many phone calls.
It seemed that without warning the system started screaming so loud that the workers had to cover their ears.
By the end of the week the power pack was back. We tried all sorts of things to resolve the problem and each thing we tried we thought it was fixed, only to discover that within a few days it would start playing up again with the ear shattering noise.
In the end we admitted defeat and re reimbursed the client in full.
For me, at the beginning of my hydraulic career it was a huge blow and I considered that maybe I was not cut out for a future in hydraulics.
But you eventually move on and get bad experiences behind you with more successful jobs. However when I come across an application with two Relief valves in the same circuit I feel that familiar sickness again envelope my being.
Regards
Bob
more on www.hydraulicbrain.com
Monday 8 August 2011
What is Regen?
Regenerative (Regen):
This often causes a little confusion with newcomers to hydraulics and I hope that I can make it easy to understand. We use the Regen circuit when we need a fast extend e.g approach cycle on a machine tool. Very simply, when extending we only displace the rod volume not the cylinder volume.
This means that the rod will move out faster but will have a much reduced force due to its area.
When we reach the point where we need the large force then we can switch out the Regen and apply pressure over the whole piston area. The ram will now move slower but we only need force not speed. Regen can only work on the extend stroke, however the ram will return quickly due to the anular area.
Be careful! with too large a rod the benefits may not be worth while. If rods are too small the force may not be large enough to overcome seal friction.
Bob
Read more about Regen on www.hydraulicbrain.com
This often causes a little confusion with newcomers to hydraulics and I hope that I can make it easy to understand. We use the Regen circuit when we need a fast extend e.g approach cycle on a machine tool. Very simply, when extending we only displace the rod volume not the cylinder volume.
This means that the rod will move out faster but will have a much reduced force due to its area.
When we reach the point where we need the large force then we can switch out the Regen and apply pressure over the whole piston area. The ram will now move slower but we only need force not speed. Regen can only work on the extend stroke, however the ram will return quickly due to the anular area.
Be careful! with too large a rod the benefits may not be worth while. If rods are too small the force may not be large enough to overcome seal friction.
Bob
Read more about Regen on www.hydraulicbrain.com
Thursday 4 August 2011
The Pump Coupling
In my early apprenticeship days a common task was to fit the pump to the motor. A simple task I hear you say. In those days it could take several hours because the motor and pump were bolted onto machined pads and had to be shimmed to get the coupling spot on line. The coupling had 4 rubber covered pins that were inserted into the mating half that had to have a small amount of movement. Our key fitting skills were also put to the test using micrometer blue to ensure a good fit.
One day we were given a different type of coupling called a “Taperloc”. It was so easy to fit and did not rely on the great accuracy and filing skills.
Since those days couplings have become easier to fit and Bell housings make it simple and more reliable.
There are still areas where we need to take care. Most pumps do not like Belt drives because the front bearing is not fit for the heavy side loading. However you can obtain easy use bearing units that fit neatly onto the pump.
I have had a pump shaft spline fail on motor a of 200Kw and created vibrations so severe that a structural engineers was called in to examine the building for damage.
Couplings are extremely important and often we tend to give them second thought.
Bob
Read more on www.hydraulicbrain.com
One day we were given a different type of coupling called a “Taperloc”. It was so easy to fit and did not rely on the great accuracy and filing skills.
Since those days couplings have become easier to fit and Bell housings make it simple and more reliable.
There are still areas where we need to take care. Most pumps do not like Belt drives because the front bearing is not fit for the heavy side loading. However you can obtain easy use bearing units that fit neatly onto the pump.
I have had a pump shaft spline fail on motor a of 200Kw and created vibrations so severe that a structural engineers was called in to examine the building for damage.
Couplings are extremely important and often we tend to give them second thought.
Bob
Read more on www.hydraulicbrain.com
Thursday 28 July 2011
Hot Systems
Where ever possible we like to avoid having to fit coolers to hydraulic systems. The cause of a hot system can be boiled down to one thing, wasted energy.
It is possible to waste energy in many ways and I would guess that the most common for hydraulic systems is blowing oil across a relief valve.
No hydraulic system is 100% efficient and any inefficiency will result in heat generation but often this can often be kept to a minimum and dissipated by convection and radiation. A large tank can help ensuring good air flow around its surfaces.
Pumps can play a significant role. Variable displacement pumps can provide the exact amount of flow needed without wasting fluid across the relief valve.
System design is critical in preventing heat generation by using unloading circuits, accumulators and correct sizing of components.
Regards
Bob
More at www.hydraulicbrain.com
It is possible to waste energy in many ways and I would guess that the most common for hydraulic systems is blowing oil across a relief valve.
No hydraulic system is 100% efficient and any inefficiency will result in heat generation but often this can often be kept to a minimum and dissipated by convection and radiation. A large tank can help ensuring good air flow around its surfaces.
Pumps can play a significant role. Variable displacement pumps can provide the exact amount of flow needed without wasting fluid across the relief valve.
System design is critical in preventing heat generation by using unloading circuits, accumulators and correct sizing of components.
Regards
Bob
More at www.hydraulicbrain.com
Thursday 21 July 2011
Getting great traffic to our new site
We launched our new website only a couple of months ago and I am thrilled with the traffic and response we are getting.
I am continuing to add more and more hydraulic content and intend to make this the largest hydraulic website available and help those with hydraulic problems, involved with dsign or are trying to learn more about the subject.
Those that have not visited the site please give it a try for Free!
Check out www.hydraulicbrain.com
All your comments are very welcome.
Thanks
Bob
I am continuing to add more and more hydraulic content and intend to make this the largest hydraulic website available and help those with hydraulic problems, involved with dsign or are trying to learn more about the subject.
Those that have not visited the site please give it a try for Free!
Check out www.hydraulicbrain.com
All your comments are very welcome.
Thanks
Bob
Why Rams Creep
So often I come across the problem of rams that creep out and this can be due to a few reasons.
Using a control valve with a centre position of all ports blocked is the most common cause. With this valve the blanked P port is under pressure and some leakage will pass either side to A&B, this will extend by displacing the rod area.
Another cause can be temperature. When the ram is locked in position using PO check valves or ball valves any temperature rise in the oil will cause expansion. If the piston seal is not 100% leak free the ram will creep forward. Without piston leakage the pressure could rise to an alarming value and cause damage to the ram.
Any load on a ram will make it creep over time. All valves have metal to metal sealing and the oil is the source of lubrication and leakage. As the running parts wear the leakage will increase and the ram will creep even more.
Always best to design with leakage in mind.
Cheers
Bob
More hydraulic stuff on www.hydraulicbrain.com
Using a control valve with a centre position of all ports blocked is the most common cause. With this valve the blanked P port is under pressure and some leakage will pass either side to A&B, this will extend by displacing the rod area.
Another cause can be temperature. When the ram is locked in position using PO check valves or ball valves any temperature rise in the oil will cause expansion. If the piston seal is not 100% leak free the ram will creep forward. Without piston leakage the pressure could rise to an alarming value and cause damage to the ram.
Any load on a ram will make it creep over time. All valves have metal to metal sealing and the oil is the source of lubrication and leakage. As the running parts wear the leakage will increase and the ram will creep even more.
Always best to design with leakage in mind.
Cheers
Bob
More hydraulic stuff on www.hydraulicbrain.com
Sunday 10 July 2011
Quick release couplings
Quick Release Couplings can be extremely useful for applications where you are frequently connecting and disconnecting hoses; however they can also present some serious problems.
I have experienced occasion ions where the coupling has become worn or damaged (often by being thrown about on the floor) and will either only partially open or in the worst case will not open at all.
These couplings rely on a mechanical valve being forced open when pushed together. By their nature they often have a high pressure drop and also are an ideal source for dirt and contaminant to enter the system.
There have even been occasions on some systems when they become hydraulically locked and will not open.
I have nothing personal against quick release couplings, all I say is use them only where absolutely necessary, protect them from damage and keep them scrupulously clean.
Very best
Bob
www.hydraulicbrain.com
I have experienced occasion ions where the coupling has become worn or damaged (often by being thrown about on the floor) and will either only partially open or in the worst case will not open at all.
These couplings rely on a mechanical valve being forced open when pushed together. By their nature they often have a high pressure drop and also are an ideal source for dirt and contaminant to enter the system.
There have even been occasions on some systems when they become hydraulically locked and will not open.
I have nothing personal against quick release couplings, all I say is use them only where absolutely necessary, protect them from damage and keep them scrupulously clean.
Very best
Bob
www.hydraulicbrain.com
Sunday 26 June 2011
Hydraulics is Business
Some of the comments I read are to me like a fashion show. Great entertainment, interesting and above all, fun. But not something I would want to wear myself. Sometimes we stray away in our daydreams to the place of fantasy (not a bad thing). But speaking only for myself, I am in business and the bottom line for me is “can I make a profit”
Now I can hear many members yawning or crying Luddite! but I am sorry chaps but that is the end game for me however I am not sure I would be able to earn my money in any other more interesting way.
During my career I have worked for some very high profile hydraulic companies and been involved in R&D on important military projects. At one time I was the least qualified in an office of 10-12 everyone bar me had a PhD and the maths were eyewatering! These were engineers that became good friends and whom I had the highest respect for. But even they at times got it wrong and when they did they got it wrong big time!
When I started to work for myself I stuck to simple KISS. The bigger the system the simpler I made it. The more complicated the system I would let someone else take the glory. Getting it wrong costs me hard earned cash! and I am not in it for the academic journey.
I apologise if I have upset anyone with my simple and basic way of business and it might seem very boring to others and over nearly 50 years I am still learning the basics and still loads to learn about but for those more adventurous, Bon voyage.
www.hydraulicbrain.com
Now I can hear many members yawning or crying Luddite! but I am sorry chaps but that is the end game for me however I am not sure I would be able to earn my money in any other more interesting way.
During my career I have worked for some very high profile hydraulic companies and been involved in R&D on important military projects. At one time I was the least qualified in an office of 10-12 everyone bar me had a PhD and the maths were eyewatering! These were engineers that became good friends and whom I had the highest respect for. But even they at times got it wrong and when they did they got it wrong big time!
When I started to work for myself I stuck to simple KISS. The bigger the system the simpler I made it. The more complicated the system I would let someone else take the glory. Getting it wrong costs me hard earned cash! and I am not in it for the academic journey.
I apologise if I have upset anyone with my simple and basic way of business and it might seem very boring to others and over nearly 50 years I am still learning the basics and still loads to learn about but for those more adventurous, Bon voyage.
www.hydraulicbrain.com
Hydraulics are so simple?
I once had a customer who told me that there was nothing difficult about hydraulics and it was pretty simple stuff and hinted that my work was over rated. I smiled and obviously could not agree because the fascination of “Fluid power” is that no matter how long you work in the business you NEVER stop learning. These forums prove that and are great value to me for picking up other people’s tips and experiences.
I will like to briefly tell you of an experience I had a couple of years ago.
I designed a small system for a “Super Yacht” to control the transom door that turns into a platform at the stern of the boat with two polished stainless steel rams . (Very expensive stuff!)
I purchased a small DC pack with pump. Motor, control valve and reservoir. When I operated the system it worked beautifully for just a short time and then stopped. I checked everything, control signal, valve, but could find nothing wrong. I drained the tank and checked the pump and everything was in order. It would start work for a few minutes and then stop.
3 days later I had changed the pump, valve, housing and electric motor and I still the same problem. I felt that I should take up a different career (so did my customer)
I decided to remove the tank for the 10th time and I sat there staring at the stripped down parts. I ran my hand around the empty tank pondering the problem almost in a dream like trance. Suddenly my hand felt something strange and my attention quickly snapped into curiosity. I carefully picked away a piece of polythene about 50 mm square a piece of left over packaging. This would stick to the side of the tank (undetected) when empty and gently float off and cover my suction port when filled with oil.
It was a “wake up call” never think you know everything!
www.hydraulicbrain.com
I will like to briefly tell you of an experience I had a couple of years ago.
I designed a small system for a “Super Yacht” to control the transom door that turns into a platform at the stern of the boat with two polished stainless steel rams . (Very expensive stuff!)
I purchased a small DC pack with pump. Motor, control valve and reservoir. When I operated the system it worked beautifully for just a short time and then stopped. I checked everything, control signal, valve, but could find nothing wrong. I drained the tank and checked the pump and everything was in order. It would start work for a few minutes and then stop.
3 days later I had changed the pump, valve, housing and electric motor and I still the same problem. I felt that I should take up a different career (so did my customer)
I decided to remove the tank for the 10th time and I sat there staring at the stripped down parts. I ran my hand around the empty tank pondering the problem almost in a dream like trance. Suddenly my hand felt something strange and my attention quickly snapped into curiosity. I carefully picked away a piece of polythene about 50 mm square a piece of left over packaging. This would stick to the side of the tank (undetected) when empty and gently float off and cover my suction port when filled with oil.
It was a “wake up call” never think you know everything!
www.hydraulicbrain.com
Friday 24 June 2011
Decompression
With large rams you might need to consider decompression.
We know that oil compresses at around 0.5% of volume per 1000psi.
A large volume ram can have a considerable volume of compressed oil and when suddenly released through the control valve may cause a bit of a bang!
This can be reduced by a decompression valve that allows the pressure to bleed off more slowly before allowing the main valve to fully open.
Some Pilot operated check valves have this feature and some control valve spools have flats ground onto the leading edges.
I remember years ago when we needed to get ourselves out of trouble we would take the spool to the hand grinder. But best not mention this to anyone!
Very best
Bob
We know that oil compresses at around 0.5% of volume per 1000psi.
A large volume ram can have a considerable volume of compressed oil and when suddenly released through the control valve may cause a bit of a bang!
This can be reduced by a decompression valve that allows the pressure to bleed off more slowly before allowing the main valve to fully open.
Some Pilot operated check valves have this feature and some control valve spools have flats ground onto the leading edges.
I remember years ago when we needed to get ourselves out of trouble we would take the spool to the hand grinder. But best not mention this to anyone!
Very best
Bob
Monday 20 June 2011
Changing the Pressure on a Machine
I was called out a few days ago to look at a tube bending machine.
The machine was PLC controlled and runs with a semi automatic program. The client has a problem bending a large steel pipe and asked if I could help. The machine was second hand with no manual so I had to quickly start from basics. The pressure was set to the highest value and the machine did not quite have the full force needed to complete the bend although it was just possible by switching the control valve off and back on again to achieve a pressure spike.
It would be possible to change the spring in the relief valve (to higher rating) but then the vane pump had a maximum of 140bar and the existing pressure is pretty close. Then there is the electric motor. By increasing the pressure we will need to draw more power and without knowing the flow and the motor Kw I could not calculate what my motor draw. Last of all I should also consider the mechanical strength of the machine. Will it take the extra load without breaking something?
Raising the pressure is a very easy thing to do but not before you have considered all of the implications.
Regards
Bob
The machine was PLC controlled and runs with a semi automatic program. The client has a problem bending a large steel pipe and asked if I could help. The machine was second hand with no manual so I had to quickly start from basics. The pressure was set to the highest value and the machine did not quite have the full force needed to complete the bend although it was just possible by switching the control valve off and back on again to achieve a pressure spike.
It would be possible to change the spring in the relief valve (to higher rating) but then the vane pump had a maximum of 140bar and the existing pressure is pretty close. Then there is the electric motor. By increasing the pressure we will need to draw more power and without knowing the flow and the motor Kw I could not calculate what my motor draw. Last of all I should also consider the mechanical strength of the machine. Will it take the extra load without breaking something?
Raising the pressure is a very easy thing to do but not before you have considered all of the implications.
Regards
Bob
Friday 17 June 2011
New Linkedin forum
I have just launched on new forum on Linkedin.
The purpose of the group is to help and support each other on issues relating to Fluid Power.
Due to the platform used, where the only method of communication is print extra effort must be made to ensure that the message sent to the recipient and the group should appear friendly, helpful and positive to the discussion.
We hope to have fun, make good friends and learn about other members Fluid power experiences.
Please come and join us.
The name of our forum is "Hydraulic help"
Cheers
Bob
The purpose of the group is to help and support each other on issues relating to Fluid Power.
Due to the platform used, where the only method of communication is print extra effort must be made to ensure that the message sent to the recipient and the group should appear friendly, helpful and positive to the discussion.
We hope to have fun, make good friends and learn about other members Fluid power experiences.
Please come and join us.
The name of our forum is "Hydraulic help"
Cheers
Bob
Wednesday 15 June 2011
Controlling Speed
There are many ways to control the speed of a hydraulic ram or motor.
We could use a pump that delivers a variable flow (variable piston or vane pump)
The easiest way is to fit a flow control valve but the question comes where do you fit it?
Meter out: This is where a valve is fitted to each leg of the mover. The arrow for free flow should point towards the mover port. The flow is restricted on the return leg back to the control valve. This will prevent the load running ahead of the oil supply and keep the system stiff. However if screwed down too far can cause some intensification on the annular side of the ram.
Meter in: Good when the mover is pushing against a load but not if the load is trying to pull the ram. Imagine pushing a car up a hill. The best place to push is behind the car. As the car reaches the summit you need to move to the front to stop the car running away. The valve should be fitted with the free flow arrow pointing away from the mover towards the control valve.
Bleed off: This can be fitted on any leg of the mover or the main pressure line.
The valve is piped to tank and bleed oil off the main flow. This can be problematic and will not give a wide range of speed control. One main benefit is that it is less prone to generate heat.
Flow control on Pressure inlet: The valve would be a simple needle valve type.
Will cause heat generation. Excess oil will pass across the relief valve.
If you are unsure what is the best way for your system please send me an email.
I will write more on this subject including, pressure and temperature compensation and Load Sensing.
See more on www.hydraulicbrain.com
Cheers
Bob
We could use a pump that delivers a variable flow (variable piston or vane pump)
The easiest way is to fit a flow control valve but the question comes where do you fit it?
Meter out: This is where a valve is fitted to each leg of the mover. The arrow for free flow should point towards the mover port. The flow is restricted on the return leg back to the control valve. This will prevent the load running ahead of the oil supply and keep the system stiff. However if screwed down too far can cause some intensification on the annular side of the ram.
Meter in: Good when the mover is pushing against a load but not if the load is trying to pull the ram. Imagine pushing a car up a hill. The best place to push is behind the car. As the car reaches the summit you need to move to the front to stop the car running away. The valve should be fitted with the free flow arrow pointing away from the mover towards the control valve.
Bleed off: This can be fitted on any leg of the mover or the main pressure line.
The valve is piped to tank and bleed oil off the main flow. This can be problematic and will not give a wide range of speed control. One main benefit is that it is less prone to generate heat.
Flow control on Pressure inlet: The valve would be a simple needle valve type.
Will cause heat generation. Excess oil will pass across the relief valve.
If you are unsure what is the best way for your system please send me an email.
I will write more on this subject including, pressure and temperature compensation and Load Sensing.
See more on www.hydraulicbrain.com
Cheers
Bob
Sunday 12 June 2011
One pump or two?
When a system requires more than one ram or motor the first question to ask is do they work at the same time. If they do you must now consider the implications. Using hand valves might just result in less speed but because oil always takes the least resistance it might stop one movement altogether.
If in doubt I prefer to use one pump for each device and then I am sure that one “mover” will not affect the other. It’s very difficult to put right if you get this wrong!
If you know a better and reliable way I would love to hear from you.
Cheers
Bob
If in doubt I prefer to use one pump for each device and then I am sure that one “mover” will not affect the other. It’s very difficult to put right if you get this wrong!
If you know a better and reliable way I would love to hear from you.
Cheers
Bob
Monday 6 June 2011
Pump Design
I am sure pump designers would love to find ways to completely eliminate, Pressure drop across the pump (with free outlet) together with, friction, noise and heat. (wasted energy) but this is the price we pay to get the flow through the pump. These are the “undesirables” of pump design we must live with (due to physics) although with better design and technology we continue to improve.
Flow is the desirable product we want from the pump and it is important that we make the pump strong enough to resist any restriction of that flow up to a maximum design pressure. After that we will likely cause damage to the pump.
So how does the pressure change within the pump?
1) By increasing pump speed (increasing the flow)
2) Changing the oil (resisting flow)
3) Adding a load (resisting flow)
4) Pipe size (resisting the flow)
And so on..
With a load sensing pump we sense a change of pressure (due to change in load) across the control valve and the pump will automatically respond and make corrections to maintain Delta P. This pressure adjustment can only be achieved by adjusting the pump flow. .
This is why we say pumps produce flow not pressure but they are designed to take pressure
Flow is the desirable product we want from the pump and it is important that we make the pump strong enough to resist any restriction of that flow up to a maximum design pressure. After that we will likely cause damage to the pump.
So how does the pressure change within the pump?
1) By increasing pump speed (increasing the flow)
2) Changing the oil (resisting flow)
3) Adding a load (resisting flow)
4) Pipe size (resisting the flow)
And so on..
With a load sensing pump we sense a change of pressure (due to change in load) across the control valve and the pump will automatically respond and make corrections to maintain Delta P. This pressure adjustment can only be achieved by adjusting the pump flow. .
This is why we say pumps produce flow not pressure but they are designed to take pressure
Thursday 2 June 2011
How would you define a pump?
How would you define a pump?
A very simple question you might think especially for a hydraulic professional.
This was the simple question posed by a young graduate on Linkedin. Over 3 months later with over 100 comments it is still being debated with some veracity.
I was always taught that pumps produce flow and pressure is a restriction of flow. A challenge to that view is that there must be a force or pressure to move any mass, therefore fluid being a mass means that if there is flow from a pump there must be pressure. I have to agree to this observation and is irrefutable.
So why don’t hydraulic people acknowledge this pressure when we know that there must be some pressure , no matter how small?.
Some things we are taught are often accepted without challenge because with a subject like hydraulics at the beginning one is trying to cope with the overall understanding without thinking of challenging the basics. These concepts eventually become accepted and fixed in one’s own mind until one day someone challenges that view.
I will give you my opinion why we ignore/deny that pumps produce pressure. I believe that by acknowledge this inbuilt load/pressure in our” definition of a pump” will it make the concept clearer or more confusing especially to those with little knowledge of the subject? I believe the latter but more than that what extra benefit does it provide to the hydraulic engineer? I suspect very little.
We know that pumps have different efficiency values. We acknowledge this in our pump power calculations. No pump is 100% and it will be reduced by friction in bearings, running gear and of course the energy needed to push the oil through the pump (also leakage). In hydraulics we factor this into our calculations and because it is a relatively small force value we often tend to ignore it. Remember that hydraulics is used to move or rotate very large loads and as a percentage of these loads the force to push the oil through the pump is very small indeed.
In future then, now that I have given more thought to this issue, how will I describe a pump? I will likely make some adjustments based on whom I am speaking to. Those starting out in hydraulic or struggling with very basic knowledge I will stick to “pumps provide flow” and for those that require a more precise definition: “A pump is a device that forces fluid through its mechanical parts to produce flow” This is wordier but I think a more accurate definition but not sure that it changes much!
Very best
Bob
A very simple question you might think especially for a hydraulic professional.
This was the simple question posed by a young graduate on Linkedin. Over 3 months later with over 100 comments it is still being debated with some veracity.
I was always taught that pumps produce flow and pressure is a restriction of flow. A challenge to that view is that there must be a force or pressure to move any mass, therefore fluid being a mass means that if there is flow from a pump there must be pressure. I have to agree to this observation and is irrefutable.
So why don’t hydraulic people acknowledge this pressure when we know that there must be some pressure , no matter how small?.
Some things we are taught are often accepted without challenge because with a subject like hydraulics at the beginning one is trying to cope with the overall understanding without thinking of challenging the basics. These concepts eventually become accepted and fixed in one’s own mind until one day someone challenges that view.
I will give you my opinion why we ignore/deny that pumps produce pressure. I believe that by acknowledge this inbuilt load/pressure in our” definition of a pump” will it make the concept clearer or more confusing especially to those with little knowledge of the subject? I believe the latter but more than that what extra benefit does it provide to the hydraulic engineer? I suspect very little.
We know that pumps have different efficiency values. We acknowledge this in our pump power calculations. No pump is 100% and it will be reduced by friction in bearings, running gear and of course the energy needed to push the oil through the pump (also leakage). In hydraulics we factor this into our calculations and because it is a relatively small force value we often tend to ignore it. Remember that hydraulics is used to move or rotate very large loads and as a percentage of these loads the force to push the oil through the pump is very small indeed.
In future then, now that I have given more thought to this issue, how will I describe a pump? I will likely make some adjustments based on whom I am speaking to. Those starting out in hydraulic or struggling with very basic knowledge I will stick to “pumps provide flow” and for those that require a more precise definition: “A pump is a device that forces fluid through its mechanical parts to produce flow” This is wordier but I think a more accurate definition but not sure that it changes much!
Very best
Bob
Wednesday 18 May 2011
Which pump?
When I first started out designing systems we had the choice between vane or piston pumps.
Gear pumps at that time were rather frowned upon and not readily available.
I haven’t used a fixed vane pump since I can remember and piston pumps only for occasions when I need high pressure or my customer is keen on quality/reliability rather than cost.
There is no doubt that the gear pump has become more popular but maybe our hydraulic group may not all agree with this trend.
Personally I will use a variable vane for those systems where I need to hold pressure for long periods with low pressure. The piston pump for higher pressure, long periods on pressure with big flows. The gear pumps for everyday low duty and competitively priced.
You will all have your own ideas for selecting the ideal pump and I would love to hear your views.
Very best
Bob
Gear pumps at that time were rather frowned upon and not readily available.
I haven’t used a fixed vane pump since I can remember and piston pumps only for occasions when I need high pressure or my customer is keen on quality/reliability rather than cost.
There is no doubt that the gear pump has become more popular but maybe our hydraulic group may not all agree with this trend.
Personally I will use a variable vane for those systems where I need to hold pressure for long periods with low pressure. The piston pump for higher pressure, long periods on pressure with big flows. The gear pumps for everyday low duty and competitively priced.
You will all have your own ideas for selecting the ideal pump and I would love to hear your views.
Very best
Bob
Saturday 7 May 2011
Tuesday 3 May 2011
Hydraulic Oil
We talk a great deal about pumps, valves, pipe-work and other hardware but give little mention about the lifeblood of the system, that of course is hydraulic oil.
This is vitally important to the life and performance of the system and come in many varieties.
When I started my career we were told to say that any oil is ok as long as it is mineral ISO 32 hydraulic oil and I suppose it is still the most common choice today.
But we also have applications where this is not suitable and today we have more choices and better oils to better suit demanding conditions.
The environment has become a greater issue and it is very important we do not contaminate the soil or waterways. Rape seed oils were common but now there are some very good synthetic oils that not only protect the environment but are better suited to the components.
Fire has long been an issue with fire resistant fluid. Water glycols must be used with overhead tanks due to specific gravity and to avoid cavitation. However there are fluids that can be used in the same way as normal oil that give similar protection.
Skydrol is used in aerospace systems and will destroy most types of rubber and plastic and need careful selection of pumps and valves.
It might be that the system is working in very hot or very cold environments and will need a suitable grade of oil that will end up with the ideal viscosity at the working temperature.
There are also oils that will not degrade when run at higher temperatures.
With mineral oils, I do not like temperatures above 50centigrade (comfortable to the touch).
Higher temperatures can cause many problems with seals, varnishing and eventually breakdown of the additives that protect the systems.
I would like to hear about oils that our group has used and maybe stories of problems when unsuitable oil is used.
Cheers
Bob
This is vitally important to the life and performance of the system and come in many varieties.
When I started my career we were told to say that any oil is ok as long as it is mineral ISO 32 hydraulic oil and I suppose it is still the most common choice today.
But we also have applications where this is not suitable and today we have more choices and better oils to better suit demanding conditions.
The environment has become a greater issue and it is very important we do not contaminate the soil or waterways. Rape seed oils were common but now there are some very good synthetic oils that not only protect the environment but are better suited to the components.
Fire has long been an issue with fire resistant fluid. Water glycols must be used with overhead tanks due to specific gravity and to avoid cavitation. However there are fluids that can be used in the same way as normal oil that give similar protection.
Skydrol is used in aerospace systems and will destroy most types of rubber and plastic and need careful selection of pumps and valves.
It might be that the system is working in very hot or very cold environments and will need a suitable grade of oil that will end up with the ideal viscosity at the working temperature.
There are also oils that will not degrade when run at higher temperatures.
With mineral oils, I do not like temperatures above 50centigrade (comfortable to the touch).
Higher temperatures can cause many problems with seals, varnishing and eventually breakdown of the additives that protect the systems.
I would like to hear about oils that our group has used and maybe stories of problems when unsuitable oil is used.
Cheers
Bob
Sunday 1 May 2011
Valve leakage
I hear a lot of myths surrounding leakage.
There have been many times when I have been asked to design a system where the client wants to hold a load almost indefinitely (leak free).
Most sliding valves need some leakage for lubrication due to metal to metal contact. Poppet valves or seated valves are as good as the next particle of contamination that lodges under the seat. Soft seated valves can give better chance of success but are less available.
The all ports blocked CETOP valve can cause problems with creeping rams. P port being close to A&B with T ports on the far side will allow pressure to A&B and send the ram out. The only remedy is either install a new valve or change to a P to T and a PO check.
Also in the attempt to lock off a load (hydraulicaly) can be dangerous. Any oil passing over the piston and with no route to tank will cause pressure intensification that might be well above the maximum allowed.
I have never relied on valves being leak free and always play safe.
Love to hear your views
Bob
There have been many times when I have been asked to design a system where the client wants to hold a load almost indefinitely (leak free).
Most sliding valves need some leakage for lubrication due to metal to metal contact. Poppet valves or seated valves are as good as the next particle of contamination that lodges under the seat. Soft seated valves can give better chance of success but are less available.
The all ports blocked CETOP valve can cause problems with creeping rams. P port being close to A&B with T ports on the far side will allow pressure to A&B and send the ram out. The only remedy is either install a new valve or change to a P to T and a PO check.
Also in the attempt to lock off a load (hydraulicaly) can be dangerous. Any oil passing over the piston and with no route to tank will cause pressure intensification that might be well above the maximum allowed.
I have never relied on valves being leak free and always play safe.
Love to hear your views
Bob
Tuesday 26 April 2011
New Fault Finding Website
New hydraulic Website www.hydraulicbrain.com
I have just launched a new website that will diagnose hydraulic problems in an interesting and novel way. www.hydraulicbrain.com.
I would like to thank Neil Dawson for the fantastic job done in producing everything I asked and hoped for, on time and at a superb price.
Thanks again Neil and I will recommend you to all who know me. amit.kum.rout@gmail.com
I would be most greatful if anyone from our group would take a look and send me their comments, opinions and how I might improve on what we have done so far.
Many thanks
Bob
I have just launched a new website that will diagnose hydraulic problems in an interesting and novel way. www.hydraulicbrain.com.
I would like to thank Neil Dawson for the fantastic job done in producing everything I asked and hoped for, on time and at a superb price.
Thanks again Neil and I will recommend you to all who know me. amit.kum.rout@gmail.com
I would be most greatful if anyone from our group would take a look and send me their comments, opinions and how I might improve on what we have done so far.
Many thanks
Bob
Sunday 17 April 2011
Hot Systems
Whenever I check out a hydraulic system my first reaction is to cautiously touch the side of the tank.
If I can comfortably keep my hand on the side I know that the system is running at a good temperature 20-30C (50-60Cmaximum). If my hand recoils due to the high temperature I know straight away that there is a potential problem.
Hot oil causes all sorts of problems and affect, seals, oil viscosity, oil degradation and the danger of scalding.
Ensuring that the system is running at the right temperature should be done at the drawing board stage and not tagged on later as an afterthought.
Things to consider are:
Installed Power
Duty cycle
Ambient temperature
Size of tank
Heat comes from the inefficiency of the system. If we do not use all the energy we are generating in doing work the rest will be converted into heat. Conversely, you will not generate any more heat than the maximum power of the prime mover.
Relief valves are the prime source for heat generation and if possible the system should be designed to minimise the length of time oil passes over this valve. Open centre control valves, pressure compensated pumps and unloading valves can help.
Some heat is radiated by the tank and can often remove the need for a cooler.
This is a huge subject, ranging from the damage heat can cause to the best types of coolers and I know that there are many in our group who will have some very interesting views on this subject.
Cheers
Bob
If I can comfortably keep my hand on the side I know that the system is running at a good temperature 20-30C (50-60Cmaximum). If my hand recoils due to the high temperature I know straight away that there is a potential problem.
Hot oil causes all sorts of problems and affect, seals, oil viscosity, oil degradation and the danger of scalding.
Ensuring that the system is running at the right temperature should be done at the drawing board stage and not tagged on later as an afterthought.
Things to consider are:
Installed Power
Duty cycle
Ambient temperature
Size of tank
Heat comes from the inefficiency of the system. If we do not use all the energy we are generating in doing work the rest will be converted into heat. Conversely, you will not generate any more heat than the maximum power of the prime mover.
Relief valves are the prime source for heat generation and if possible the system should be designed to minimise the length of time oil passes over this valve. Open centre control valves, pressure compensated pumps and unloading valves can help.
Some heat is radiated by the tank and can often remove the need for a cooler.
This is a huge subject, ranging from the damage heat can cause to the best types of coolers and I know that there are many in our group who will have some very interesting views on this subject.
Cheers
Bob
Sunday 10 April 2011
Suppliers get 90% of our orders wrong!
All the financial experts are saying that the small amount of manufacturing we still have is picking up and no one can be more pleased to hear that than me. But with this welcome successes comes other problems.
In my business and I dare say many other similar businesses are now suffering long delivery or poor quality issues. I would go even further and say that 90% of the orders we place with suppliers we are either told the parts are no longer available, have long delivery times or just comes in wrong!
These days many components are not made in the Uk and we are reliant on overseas manufacturers. Anything we need from Germany and I’ll bet it will be as difficult to get as hen’s teeth and a big price tag to boot. When the world’s economies pick up it is not surprising that manufacturers look after their home markets first. Although we can now get some of those important orders we craved, it is the delivery issues that are letting us down and disappointing our customers.
What I find most frustrating is when orders come in wrong either due to poor workmanship or simply the sales guy has not paid proper attention to my needs. Recently, after waiting 3 weeks for my supplier to deliver some urgent parts and continuous chasing by phone and email he admitted that he had forgotten to place the order on his factory floor.
If we are to get serious again about Manufacturing we must get it right. Saying sorry is just not good enough and does not excuse sloppy service and it will certainly not get us back as a serious world competitor. We also need to be more self sufficient in obtaining simple parts to prevent hold ups, improve our cash flow and make us more price competitive.
To do that of course we must also have stability and continued commitment from our Government to ensure we get the investment in skills and equipment for the long term, and then hopefully this resurgence will not be just a flash in the pan.
Cheers
Bob
In my business and I dare say many other similar businesses are now suffering long delivery or poor quality issues. I would go even further and say that 90% of the orders we place with suppliers we are either told the parts are no longer available, have long delivery times or just comes in wrong!
These days many components are not made in the Uk and we are reliant on overseas manufacturers. Anything we need from Germany and I’ll bet it will be as difficult to get as hen’s teeth and a big price tag to boot. When the world’s economies pick up it is not surprising that manufacturers look after their home markets first. Although we can now get some of those important orders we craved, it is the delivery issues that are letting us down and disappointing our customers.
What I find most frustrating is when orders come in wrong either due to poor workmanship or simply the sales guy has not paid proper attention to my needs. Recently, after waiting 3 weeks for my supplier to deliver some urgent parts and continuous chasing by phone and email he admitted that he had forgotten to place the order on his factory floor.
If we are to get serious again about Manufacturing we must get it right. Saying sorry is just not good enough and does not excuse sloppy service and it will certainly not get us back as a serious world competitor. We also need to be more self sufficient in obtaining simple parts to prevent hold ups, improve our cash flow and make us more price competitive.
To do that of course we must also have stability and continued commitment from our Government to ensure we get the investment in skills and equipment for the long term, and then hopefully this resurgence will not be just a flash in the pan.
Cheers
Bob
Sunday 3 April 2011
Hydraulic Circuit Conventions
Fault finding hydraulic systems can be difficult but much harder without the benefit of an accurate circuit diagram.
Many systems are very simple, a pump, relief and directional control valve. This is straight forward and easy to follow but more complex systems with large manifolds can be almost impossible without the benefit of a circuit.
To the un- initiated eye, circuit diagrams can look like something written by a creature from a distant planet but circuit diagrams and symbols are quite easy to understand.
I always say to students that hydraulic symbols are similar to road signs and will resemble the components it represents. (a spring looks like a spring, a flow path an arrow)
What I find irritating and most annoying is when I pick up a circuit drawing that has come from a well known International hydraulic company that have symbols I do not recognise or maybe a Relief valve drawn instead of a Reducing valve. I even see symbols that have been made up, created and nothing I have ever seen in ISO or CETOP standards.
Many of us would not be particularly fazed by a Relief Valve being misplaced by a Reducer because of it’s the location in the circuit. but on my complex circuits, non standard symbols can be confusing and result in a lot of head scratching and wasted time.
Like any engineering drawing, circuit drawings should be clear, unambiguous and follow proper International standards. If we all start designing own symbols and drawing circuits without proper convention it could at best be more confusing and at worst cause serious accidents. Employers should ensure that their engineers are doing things right and setting standards that we can all understand.
I would love to hear your views; maybe you have misread a drawing?
Cheers
Bob
Many systems are very simple, a pump, relief and directional control valve. This is straight forward and easy to follow but more complex systems with large manifolds can be almost impossible without the benefit of a circuit.
To the un- initiated eye, circuit diagrams can look like something written by a creature from a distant planet but circuit diagrams and symbols are quite easy to understand.
I always say to students that hydraulic symbols are similar to road signs and will resemble the components it represents. (a spring looks like a spring, a flow path an arrow)
What I find irritating and most annoying is when I pick up a circuit drawing that has come from a well known International hydraulic company that have symbols I do not recognise or maybe a Relief valve drawn instead of a Reducing valve. I even see symbols that have been made up, created and nothing I have ever seen in ISO or CETOP standards.
Many of us would not be particularly fazed by a Relief Valve being misplaced by a Reducer because of it’s the location in the circuit. but on my complex circuits, non standard symbols can be confusing and result in a lot of head scratching and wasted time.
Like any engineering drawing, circuit drawings should be clear, unambiguous and follow proper International standards. If we all start designing own symbols and drawing circuits without proper convention it could at best be more confusing and at worst cause serious accidents. Employers should ensure that their engineers are doing things right and setting standards that we can all understand.
I would love to hear your views; maybe you have misread a drawing?
Cheers
Bob
Saturday 2 April 2011
Designing for the environment
Drawing a hydraulic circuit and working out the sizes for pumps, valves and actuator are very important but not the beginning and end all. Just as important is where the equipment will be used and the environmental implications of the design.
Foundries and steel mills can be very dirty places and also not a place where you want a hose to burst, spraying hydraulic oil across molten metal.
Any system close to the sea, on a boat or oil rig will suffer from high levels of corrosion. Maybe you should be thinking of stainless steel pipe-work or epoxy painted surfaces. Also boats and mobile equipment might prefer smaller oil reservoirs and closed circuit pumps.
The yacht enthusiast are very concerned about weight, again watch out for large oil tanks.
Consider special materials, titanium, aluminium and carbon fibre and it might even be that the system must be able to work upside down without spillage!
Mobile equipment often needs to be light. Rams might have to be smaller with higher pressure to achieve the same forces..
Many industries like heavy duty, robust equipment that can be abused. Watch out for vulnerable components like electronic instruments. (Transducers can be fitted inside the rams)
Hydraulics used in some environments must not spill mineral oil onto water or the soil. Consider synthetic environmental friendly oils.
There are some applications where noise is a problem. Film sets and close proximity to public places that are very sensitive noise. Using quieter pumps, hydraulic hose, accumulators and attenuators might be an option.
If you are designing a system to be used in a hot environment with very high ambient temperature or humidity. Sometimes water cooling is just NOT an option.
In summary, I am saying that there are many different levels of a hydraulic design and they all have equal importance. The environment can be crucial to the success or failure of your design. Ignore it at your peril!.
I would love to hear about your views or any stories you might have where the environment was a major issue.
Cheers
Bob
Foundries and steel mills can be very dirty places and also not a place where you want a hose to burst, spraying hydraulic oil across molten metal.
Any system close to the sea, on a boat or oil rig will suffer from high levels of corrosion. Maybe you should be thinking of stainless steel pipe-work or epoxy painted surfaces. Also boats and mobile equipment might prefer smaller oil reservoirs and closed circuit pumps.
The yacht enthusiast are very concerned about weight, again watch out for large oil tanks.
Consider special materials, titanium, aluminium and carbon fibre and it might even be that the system must be able to work upside down without spillage!
Mobile equipment often needs to be light. Rams might have to be smaller with higher pressure to achieve the same forces..
Many industries like heavy duty, robust equipment that can be abused. Watch out for vulnerable components like electronic instruments. (Transducers can be fitted inside the rams)
Hydraulics used in some environments must not spill mineral oil onto water or the soil. Consider synthetic environmental friendly oils.
There are some applications where noise is a problem. Film sets and close proximity to public places that are very sensitive noise. Using quieter pumps, hydraulic hose, accumulators and attenuators might be an option.
If you are designing a system to be used in a hot environment with very high ambient temperature or humidity. Sometimes water cooling is just NOT an option.
In summary, I am saying that there are many different levels of a hydraulic design and they all have equal importance. The environment can be crucial to the success or failure of your design. Ignore it at your peril!.
I would love to hear about your views or any stories you might have where the environment was a major issue.
Cheers
Bob
Wednesday 30 March 2011
Stop Hydraulic Leaks
How do we stop Leaks?
When I run hydraulic courses I ask students what they believe are the benefits and disadvantages of hydraulics. Putting aside the benefits, the largests negative is messy oil leaks.
You would think that after all these years we would have come up with a 100% foolproof method of preventing leaks.
Some methods of sealing include:
1) Nut and ferrule
2) O rings
3) Bonded washers
4) Copper washers
5) PTFE tape
6) Liquid sealants
7) Tapered threads
8) Parallel threads
9) Flared tubes
10) Flanges
I am sure there are some I have missed but all these have their good points and bad.
Hot systems can make o rings become brittle and loose elasticity.
PTFE tape is used with taper threads that can create high stress if used on parallel holes.
Bonded seals are very popular but without a good spot face and perfect finish with the lay of machining not cutting across the seal face, leaks will eventually always work through.
Finding leaks can also be an impossible task. Oil will often drip from one place run from pipe to pipe and eventually create puddle metres away from its origin. I have found that a dose of fluorescent dye put into the tank will often reveal the source under a beam of a fluorescent lamp.
Many hydraulic equipment owners would love a guaranteed leak free system, so would I, but I fear that there is not much chance in the near future unless of course you know different!
Love to hear your views and comments.
Bob
When I run hydraulic courses I ask students what they believe are the benefits and disadvantages of hydraulics. Putting aside the benefits, the largests negative is messy oil leaks.
You would think that after all these years we would have come up with a 100% foolproof method of preventing leaks.
Some methods of sealing include:
1) Nut and ferrule
2) O rings
3) Bonded washers
4) Copper washers
5) PTFE tape
6) Liquid sealants
7) Tapered threads
8) Parallel threads
9) Flared tubes
10) Flanges
I am sure there are some I have missed but all these have their good points and bad.
Hot systems can make o rings become brittle and loose elasticity.
PTFE tape is used with taper threads that can create high stress if used on parallel holes.
Bonded seals are very popular but without a good spot face and perfect finish with the lay of machining not cutting across the seal face, leaks will eventually always work through.
Finding leaks can also be an impossible task. Oil will often drip from one place run from pipe to pipe and eventually create puddle metres away from its origin. I have found that a dose of fluorescent dye put into the tank will often reveal the source under a beam of a fluorescent lamp.
Many hydraulic equipment owners would love a guaranteed leak free system, so would I, but I fear that there is not much chance in the near future unless of course you know different!
Love to hear your views and comments.
Bob
Sunday 27 March 2011
Commissioning a New Hydraulic System
In my opinion, most damage caused to any pump must surely be in the first few seconds of starting up a new system. With empty pipe-work it takes a few vital seconds to get oil into the pump and it is crucial to prevent any breakdown in the boundary lubrication of the running parts.
The Piston pump case should be filled through the drain port (ensure that the port is on top and cannot siphon back). Gear and vane pumps work better with flooded suction and remember that the suction line diameter and length must be correctly sized to avoid cavitation.
I start a new system using stop/start method, each time increasing the running time by a few more seconds. Eventually building up to full speed (tricky with engine drives but can be done).
Steel pipe-work and hoses should be flushed to avoid dangerous particles entering your brand new pump. Once the damage starts it becomes self perpetuating and can substantial decrease pump life.
DC motor systems have their own unique problems. These electric motors are often burnt out during the commissioning stage. DC motors are not continuously rated and have a maximum running time and minimum cooling period, this is often forgotten.
If you have any ideas or tips on this subject I would love to hear from you.
The Piston pump case should be filled through the drain port (ensure that the port is on top and cannot siphon back). Gear and vane pumps work better with flooded suction and remember that the suction line diameter and length must be correctly sized to avoid cavitation.
I start a new system using stop/start method, each time increasing the running time by a few more seconds. Eventually building up to full speed (tricky with engine drives but can be done).
Steel pipe-work and hoses should be flushed to avoid dangerous particles entering your brand new pump. Once the damage starts it becomes self perpetuating and can substantial decrease pump life.
DC motor systems have their own unique problems. These electric motors are often burnt out during the commissioning stage. DC motors are not continuously rated and have a maximum running time and minimum cooling period, this is often forgotten.
If you have any ideas or tips on this subject I would love to hear from you.
Friday 25 March 2011
Hydraulics in Sailing
Around 30 years ago I joined a Hydraulic Engineering Company located in Southampton.
My manager told me that he did not want business from Farmers, Yachties or Mad Inventors because they took up lots of time without much in the way of profit.
Since then, I set up my own hydraulic business and for the last 15 years marine and yachting have been extremely important to my turnover. By the way, I also became one of those Mad inventors!
Since those early days I am amazed how popular hydraulics have become to yacht designers and I have produced systems for Bow and Stern thrusters, Vang, Windlass, Lifting and Canting keels for Open 60 racing and not forgetting boat lifters located in many marinas.
The racing yachts are of special interest where the demand for lightness and reliability are of prime importance and often have technically opposing constraints. For me the greatest fun and challenge is how we need to constantly push technology by using special materials like Titanium and Carbon Fibre coupled with the latest machining methods.
Unlike my manager, in those early days I see yachting as a most exciting and growing opportunity for fluid power.
My manager told me that he did not want business from Farmers, Yachties or Mad Inventors because they took up lots of time without much in the way of profit.
Since then, I set up my own hydraulic business and for the last 15 years marine and yachting have been extremely important to my turnover. By the way, I also became one of those Mad inventors!
Since those early days I am amazed how popular hydraulics have become to yacht designers and I have produced systems for Bow and Stern thrusters, Vang, Windlass, Lifting and Canting keels for Open 60 racing and not forgetting boat lifters located in many marinas.
The racing yachts are of special interest where the demand for lightness and reliability are of prime importance and often have technically opposing constraints. For me the greatest fun and challenge is how we need to constantly push technology by using special materials like Titanium and Carbon Fibre coupled with the latest machining methods.
Unlike my manager, in those early days I see yachting as a most exciting and growing opportunity for fluid power.
Hot or Cold Oil
One of the most important conditions for any healthy hydraulic system must surely be temperature.
The number of times I have examined power-packs where you could easily fry an egg on the lid. I once heard a story (not sure how true) where a hydraulic engineer was asked to examine a very noisy system. He found that the RL filter was covered in paper labels from operators who had lowered their tins beans into the tank to warm them up for lunch. The paper labels would gently float off the can and end up on the filter.
Obviously this must have been a system that ran far too hot plus a dose of cavitation to boot.
Heat can also cause more long term problems including the breakdown of the hydraulic oil. Additives protect the components, the change in viscosity will cause increased leakage (slower speed) and seals will become brittle.
Ninety percent of the time, I find a hot systems will be down to a relief valve blowing. This creates wasted energy and is immediately converted into heat.
Cold oil is also a problem. Some systems will not work properly until they reach 20-30 degrees Centigrade. You might think that this does not cause any long term problems but cold oil can often mean thick oil and thick oil can cause cavitation (another pump killer)
It is very important to design hydraulic systems that will operate at the correct temperature and if possible without the need for special cooling.
Most of the hot systems I see are often just shear bad design or built for very low cost.
This is a very wide subject and I would love to hear about yours views and experiences.
Cheers
Bob
The number of times I have examined power-packs where you could easily fry an egg on the lid. I once heard a story (not sure how true) where a hydraulic engineer was asked to examine a very noisy system. He found that the RL filter was covered in paper labels from operators who had lowered their tins beans into the tank to warm them up for lunch. The paper labels would gently float off the can and end up on the filter.
Obviously this must have been a system that ran far too hot plus a dose of cavitation to boot.
Heat can also cause more long term problems including the breakdown of the hydraulic oil. Additives protect the components, the change in viscosity will cause increased leakage (slower speed) and seals will become brittle.
Ninety percent of the time, I find a hot systems will be down to a relief valve blowing. This creates wasted energy and is immediately converted into heat.
Cold oil is also a problem. Some systems will not work properly until they reach 20-30 degrees Centigrade. You might think that this does not cause any long term problems but cold oil can often mean thick oil and thick oil can cause cavitation (another pump killer)
It is very important to design hydraulic systems that will operate at the correct temperature and if possible without the need for special cooling.
Most of the hot systems I see are often just shear bad design or built for very low cost.
This is a very wide subject and I would love to hear about yours views and experiences.
Cheers
Bob
Wednesday 23 March 2011
2011 Budget
"Made in Britain,designed in Britain, created in Britain and invented in Britain"
I'm all for that!
I'm all for that!
Monday 21 March 2011
Pipe-work and Hoses
When I first started out in hydraulics, hoses were as rare as hen’s teeth.
My apprenticeship gave me many skills and the opportunity to discover various disciplines including the pipe fitting.
We bent and manipulated pipes of all sizes, including filling some pipes with sand to prevent them collapsing.
One day we were given hoses to fit and told that they were suitable for high pressure and could flex and bend, unlike steel.
Nowadays things are very different, hoses are no longer fitted just because they can bend. They are mostly fitted because of quickness and cost.
But are they better?
Steel pipe-work is often fitted for life, where hoses have a much shorter life and will need replacing. Personally I love to see well fitted steel pipe-work, it looks smart and is an integral part of the machine. Hoses often look like bird’s nests, untidy and tide on. The other day I was working on a mobile machine where I had to track the pipe-work, it was a nightmare trying to leaver the hoses apart.
Some systems require “stiffness” to provide good accuracy and steel pipe is better, however hose can provide compliance and help reduce noise and hydraulic shock.
I have no doubt that hoses have their rightful place but I also believe that we should be more discriminate and not just fit a hose because it is quick, easy to fit and cheap.
If you have views I would love to hear from you.
Cheers
Bob
My apprenticeship gave me many skills and the opportunity to discover various disciplines including the pipe fitting.
We bent and manipulated pipes of all sizes, including filling some pipes with sand to prevent them collapsing.
One day we were given hoses to fit and told that they were suitable for high pressure and could flex and bend, unlike steel.
Nowadays things are very different, hoses are no longer fitted just because they can bend. They are mostly fitted because of quickness and cost.
But are they better?
Steel pipe-work is often fitted for life, where hoses have a much shorter life and will need replacing. Personally I love to see well fitted steel pipe-work, it looks smart and is an integral part of the machine. Hoses often look like bird’s nests, untidy and tide on. The other day I was working on a mobile machine where I had to track the pipe-work, it was a nightmare trying to leaver the hoses apart.
Some systems require “stiffness” to provide good accuracy and steel pipe is better, however hose can provide compliance and help reduce noise and hydraulic shock.
I have no doubt that hoses have their rightful place but I also believe that we should be more discriminate and not just fit a hose because it is quick, easy to fit and cheap.
If you have views I would love to hear from you.
Cheers
Bob
Friday 18 March 2011
Po check or Counterbalance
The Pilot Operated Check and Counterbalance valve are not only different in construction they are also different in their use.
The POC is a normally closed valve that is primarily used for holding a load. It is a poppet valve held down onto a seat by a spring. The valve can be lifted off its seat by a small piston and the pilot pressure created in the in- put leg of the circuit. Like all check valves they can be sharp acting and unstable if fitted inappropriately.
The Counterbalance valve is a spool valve normally closed and piloted to open by pressure in the in- put leg of the circuit to the actuator. The big difference is that the valve will modulate (move back and forth), open or close in proportion to the pilot pressure. This valve is designed to stop the load running away. If the load tries to move ahead of the input flow to the actuator, the pilot pressure will reduce and restrict the output flow thus checking the speed.
Also the valve has an added feature of a relief valve that will prevent over pressure.
Comparing the POC with Counterbalance, the latter is far more controlled with a much smoother operation but I have found them to be more susceptible to failure than the POC and can often render a situation with a load stranded in the air.
Over the years I have experimented and replaced the CBV with a POC. To provide the same effect it is also important to install a relief valve on the holding side (Pressure to tank) and a flow control to stop the load from racing away ahead of the input flow. The only downside with this set up is that there is the danger of the relief valve failing open and it is not ideal for a varying load unless you use a pressure compensated flow control valve. Otherwise I found the system to be more reliable and less prone to leaking. This is not suitable for all applications (where maximum safety is required) but can have its place for some applications. Imagine where it is crucial that the actuator must not get stuck in a dangerous position.
If you have used these valves in a more unusual way or different setup or have comments regarding this subject I would be pleased to hear from you.
Cheers
Bob
The POC is a normally closed valve that is primarily used for holding a load. It is a poppet valve held down onto a seat by a spring. The valve can be lifted off its seat by a small piston and the pilot pressure created in the in- put leg of the circuit. Like all check valves they can be sharp acting and unstable if fitted inappropriately.
The Counterbalance valve is a spool valve normally closed and piloted to open by pressure in the in- put leg of the circuit to the actuator. The big difference is that the valve will modulate (move back and forth), open or close in proportion to the pilot pressure. This valve is designed to stop the load running away. If the load tries to move ahead of the input flow to the actuator, the pilot pressure will reduce and restrict the output flow thus checking the speed.
Also the valve has an added feature of a relief valve that will prevent over pressure.
Comparing the POC with Counterbalance, the latter is far more controlled with a much smoother operation but I have found them to be more susceptible to failure than the POC and can often render a situation with a load stranded in the air.
Over the years I have experimented and replaced the CBV with a POC. To provide the same effect it is also important to install a relief valve on the holding side (Pressure to tank) and a flow control to stop the load from racing away ahead of the input flow. The only downside with this set up is that there is the danger of the relief valve failing open and it is not ideal for a varying load unless you use a pressure compensated flow control valve. Otherwise I found the system to be more reliable and less prone to leaking. This is not suitable for all applications (where maximum safety is required) but can have its place for some applications. Imagine where it is crucial that the actuator must not get stuck in a dangerous position.
If you have used these valves in a more unusual way or different setup or have comments regarding this subject I would be pleased to hear from you.
Cheers
Bob
Sunday 13 March 2011
Protecting Cylinder Rods
I have just been reading an online article/blog claiming the benefits of using shrouds and bellows to protect hydraulic cylinder rods. We moved away from this method of protection many years ago.
It became very obvious to us that shrouds and bellows created more problems than they solved.
As the bellows extend and retract they must be able to breathe often through small filters to stop contamination entering. These small filters can easily block with the result of damaged bellows. Now it will be possible for contaminated air to enter and debris can build up creating a compacted solid mass and held in place by the bellows. This can cause considerable damage to the rod, the very thing you were trying to prevent.
Our conclusion is, do not use bellows as they make the situation worse.
You may have a different view that I will be pleased to hear
It became very obvious to us that shrouds and bellows created more problems than they solved.
As the bellows extend and retract they must be able to breathe often through small filters to stop contamination entering. These small filters can easily block with the result of damaged bellows. Now it will be possible for contaminated air to enter and debris can build up creating a compacted solid mass and held in place by the bellows. This can cause considerable damage to the rod, the very thing you were trying to prevent.
Our conclusion is, do not use bellows as they make the situation worse.
You may have a different view that I will be pleased to hear
Tuesday 8 March 2011
Pipe-work v Manifold
It can be a difficult to choose between using pipe mounted valves or design and installing a manifold. There are benefits and disadvantages to both systems and here are a few.
Pipe-work (benefits)
1) Can be modified easily
2) Fault finding easier
3) Dissipates heat
Manifold block (benefits)
1) Compact and tidy
2) Fewer leaks
3) Quick and less installation skill required
When I fault find a hydraulic system it always becomes a lot more difficult with a manifold.
You cannot get in and isolate valves or test individual valves. Prototype systems often need some modifications and again the manifold can be more difficult.
Leaking pipe fittings can be a big problem with pipe-mounted valves and the more valves the more fittings and leaks.
I think that the manifold block is very much like the modern car. It’s great when everything is working well but difficult when things go wrong.
If you have some views I will be pleased to hear
Cheers
Bob
Pipe-work (benefits)
1) Can be modified easily
2) Fault finding easier
3) Dissipates heat
Manifold block (benefits)
1) Compact and tidy
2) Fewer leaks
3) Quick and less installation skill required
When I fault find a hydraulic system it always becomes a lot more difficult with a manifold.
You cannot get in and isolate valves or test individual valves. Prototype systems often need some modifications and again the manifold can be more difficult.
Leaking pipe fittings can be a big problem with pipe-mounted valves and the more valves the more fittings and leaks.
I think that the manifold block is very much like the modern car. It’s great when everything is working well but difficult when things go wrong.
If you have some views I will be pleased to hear
Cheers
Bob
Saturday 5 March 2011
The Future for Hydraulic Drives
It did not seem that long ago when I first came across a company selling a device called an inverter.
They told me that is was possible to take a standard 3 phase electric motor and vary the speed.
This was something up until then that you could only do with a hydraulic drive. Well the rest you will say, is history. We now see electrical drives of all sizes driven this way. Not only speed but torque control also.
Over recent years we have seen more and more electrical drives replace hydraulic drives. Where once a hydraulic drive was the only sensible solution there now sits a sparkling, clean, leak-free, efficient electric motor.
The only places I now see hydraulic drives now are mainly, marine and mobile applications or where power to size ratio is important.
Also electrical drives are more efficient and have considerable power savings with smoother control.
What does the future hold?
Is there an electrical linear drive around the corner that can compete with hydraulic rams, if so what is the future for Hydraulics systems?
Regards
Bob
They told me that is was possible to take a standard 3 phase electric motor and vary the speed.
This was something up until then that you could only do with a hydraulic drive. Well the rest you will say, is history. We now see electrical drives of all sizes driven this way. Not only speed but torque control also.
Over recent years we have seen more and more electrical drives replace hydraulic drives. Where once a hydraulic drive was the only sensible solution there now sits a sparkling, clean, leak-free, efficient electric motor.
The only places I now see hydraulic drives now are mainly, marine and mobile applications or where power to size ratio is important.
Also electrical drives are more efficient and have considerable power savings with smoother control.
What does the future hold?
Is there an electrical linear drive around the corner that can compete with hydraulic rams, if so what is the future for Hydraulics systems?
Regards
Bob
Friday 4 March 2011
The Law of Diminishing Returns
I have been designing systems for many years and like any Hydraulic System Designer
I try to cover every possible scenario.
We look at what might/ could happen that could affect safety of the operator or cause damage to the equipment.
Maybe you are concerned about what happens if you get a power failure or maybe an external force reacting back on the ram. It might be an event that is very unlikely to occur and you wonder if to cover it in the design or because it’s such a very rare event, take the chance!
What I am getting at here is about the sleepless nights and the myriad of extra valves you use in order to safeguard against all of those possibilities.
You then take another look at your system, it is bristling with valves and resembles an over decorated Christmas tree. You now worry that you have created a system with a greater risk of failure because of the number of parts and what about all that leakage!
We have the saying “Keep it simple stupid” kiss, but at what point do we draw the line and say we have gone far enough without compromising safety?
I try to cover every possible scenario.
We look at what might/ could happen that could affect safety of the operator or cause damage to the equipment.
Maybe you are concerned about what happens if you get a power failure or maybe an external force reacting back on the ram. It might be an event that is very unlikely to occur and you wonder if to cover it in the design or because it’s such a very rare event, take the chance!
What I am getting at here is about the sleepless nights and the myriad of extra valves you use in order to safeguard against all of those possibilities.
You then take another look at your system, it is bristling with valves and resembles an over decorated Christmas tree. You now worry that you have created a system with a greater risk of failure because of the number of parts and what about all that leakage!
We have the saying “Keep it simple stupid” kiss, but at what point do we draw the line and say we have gone far enough without compromising safety?
Thursday 24 February 2011
Changes over 45 years
I,ve been in hydraulics for over 45years and watched the industry off- load their technical sales people. We are now referred to websites to sort it out for ourselves, is this the way forward?
Sound technical product knowledge seems to be something of the past. Many sales engineers, with years of experience could offer good advice on how you could use their product. They new how much extra margine you might have on pressure or flow etc.
With few exceptions, you are now passed from pillar to post and usually end up on a website sorting it out for yourself and hoping that you have got it right.
There is nothing that gives more confidence than buying a product from an engineer who knows his stuff!
Sound technical product knowledge seems to be something of the past. Many sales engineers, with years of experience could offer good advice on how you could use their product. They new how much extra margine you might have on pressure or flow etc.
With few exceptions, you are now passed from pillar to post and usually end up on a website sorting it out for yourself and hoping that you have got it right.
There is nothing that gives more confidence than buying a product from an engineer who knows his stuff!
Pump Strainers
Those for Strainers, would claim that they prevent large particles from entering the pump via the suction pipe and anything large will almost certainly wreck the pump. A big piston pump could cost thousands of pounds.
Those against would say that strainers are 125micron and do not stop small particles. They also collect silt and fiberous material on the mesh which eventually blocks the strainer and damages the pump through cavitation. Strainers are located in the tank and owners are not always aware they exist. By the time they do, the pump can be wrecked.
Those against would say that strainers are 125micron and do not stop small particles. They also collect silt and fiberous material on the mesh which eventually blocks the strainer and damages the pump through cavitation. Strainers are located in the tank and owners are not always aware they exist. By the time they do, the pump can be wrecked.
Synchronise Rams
Synchronise Rams
Over the years I have seen many methods used to synchronise hydraulic rams, some successful and some bordering on the bazaar.
Getting rams to move together can be tricky and applications like “ A frame” cranes can be potentially dangerous if the wrong method is used.
The simplest method is to join rams together using a mechanical strut / beam that is strong enough to take any out of balance forces. We often see rams used this way on Skip Lorries where the two rams are joined together with a cross beam and the input flow split using just equal lengths of pipe work.
More accurate control can be effective with flow divider valves, gear and piston motor types. These offer more better control with accuracy between 5-10% of stroke but as wear increases these figures will also increase.
The most accurate form of synchronisation will be achieved using a servo closed loop control with linear transducer feedback. One cylinder will be driven whilst the other slaved.
I have also used NC valves with stepper motor control. Using one digital input signal to two stepper motors that drive the NC valves. This has its own inbuilt mechanical feedback mechanism that can synchronise rams to just a few microns even with an off centre load.
Over the years I have seen many methods used to synchronise hydraulic rams, some successful and some bordering on the bazaar.
Getting rams to move together can be tricky and applications like “ A frame” cranes can be potentially dangerous if the wrong method is used.
The simplest method is to join rams together using a mechanical strut / beam that is strong enough to take any out of balance forces. We often see rams used this way on Skip Lorries where the two rams are joined together with a cross beam and the input flow split using just equal lengths of pipe work.
More accurate control can be effective with flow divider valves, gear and piston motor types. These offer more better control with accuracy between 5-10% of stroke but as wear increases these figures will also increase.
The most accurate form of synchronisation will be achieved using a servo closed loop control with linear transducer feedback. One cylinder will be driven whilst the other slaved.
I have also used NC valves with stepper motor control. Using one digital input signal to two stepper motors that drive the NC valves. This has its own inbuilt mechanical feedback mechanism that can synchronise rams to just a few microns even with an off centre load.
Should you paint inside the tank
Should the inside of the tank/reservoir be painted or left bare?
This is a question I am often asked.
Leaving the tank bare risks the build up of rust and this can drop off and contaminate the oil.
Painting the tank with a good epoxy has benifits including.
1) It will seal in particles missed from cleaning (bits of weld splatter)
2) Prevents rust building up.
The issue I have with painting is if comes off (big problem!)
I have seen tanks where the lids and the sides have been painted only down to the oil line.
This is a question I am often asked.
Leaving the tank bare risks the build up of rust and this can drop off and contaminate the oil.
Painting the tank with a good epoxy has benifits including.
1) It will seal in particles missed from cleaning (bits of weld splatter)
2) Prevents rust building up.
The issue I have with painting is if comes off (big problem!)
I have seen tanks where the lids and the sides have been painted only down to the oil line.
Holding a Load
A problem that raises its head every so often is holding a load on a ram.
I don’t mean for a few minutes or even an hour I am talking about many hours or even days.
Holding a load for a short time can easily be done using a pilot operated check valve. This is probably the best valve because being a seated poppet they are less likely to leak although a little contamination under the seat can cause a problem.
On occasions I have been asked to close the ram off with ball valve, which I refuse to do.
Any leak across the piston can cause pressure intensification due to the ratio of the piston and rod area.
As far as I know there is no way of holding a load on a ram for long periods of time and it should be no surprise to raise a load one day only to see it down the next unless a mechanical locking mechanism is used.
I would like your views, maybe someone out there has other interesting ideas they can share.
Cheers
Bob
I don’t mean for a few minutes or even an hour I am talking about many hours or even days.
Holding a load for a short time can easily be done using a pilot operated check valve. This is probably the best valve because being a seated poppet they are less likely to leak although a little contamination under the seat can cause a problem.
On occasions I have been asked to close the ram off with ball valve, which I refuse to do.
Any leak across the piston can cause pressure intensification due to the ratio of the piston and rod area.
As far as I know there is no way of holding a load on a ram for long periods of time and it should be no surprise to raise a load one day only to see it down the next unless a mechanical locking mechanism is used.
I would like your views, maybe someone out there has other interesting ideas they can share.
Cheers
Bob
Thursday 10 February 2011
I was kindly sent this by Sampathkumar Iyengar showing a filter screen in a hydraulic tank. I have never seen this done before. Looks a very good idea!
Many thanks Sampathkumar
Dear Bob,
These screens serve the purpose of filtration of oil from the dirty side to the clean side of the reservoir.
These screens can be periodically removed for cleaning and re inserted in the slots.
These screens have advantage of large area of wire mesh available to trap dirt and debris from the return line of systems
For the suppression of bubbles we weld a sheet with a 45 degree slope with perforations on the side leading to the clean chamber
I am enclosing an additional photos with remarks for clarity.
Trust the information assists
Best regards
Sampathkumar Iyengar
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