I was asked to oversee the installation of a hydraulic winch system installed on a workboat and designed by (winch experts)
My client had used this company before and was very satisfied with their expertise and service. If my client was happy then so was I.
It came the day when I had to inspect the installation. There was a gear pump attached to a large diesel engine via a flexible coupling, the winch was fitted on deck and the control valve, counterbalance valve with manifold were supplied loose.
I studied the circuit and the first thing that caught my attention was the closed centre control valve. This prompted an immediate phone call to the designer, the last thing we wanted was a hot system. He assured me that the control valve supplied was in fact a Pressure to Tank configuration and that he had drawn the symbol incorrectly. I then asked him what speed had he designed the pump to run at, “1000rpm” he said.
Now under normal conditions whilst using the winch the engine speed would run at 1000rpm but when the boat steamed from one position to another the engine rpm can increase to 2100-2200rpm, more than twice the design speed and what is more important twice the design flow.
Now we have a problem!
The control valve and pipe-work was not large enough to handle this extra flow. The first suggestion by the designer was to increase the size of the control valve, an obvious solution you might think. The first problem was that it would need larger diameter hoses (difficult to get onto the valve) but more importantly the valve looses its sensitivity due to the flow gain of the larger valve. Being a proportional valve and using a joystick with electrical control the winch would not have the sensitivity and less easy to control at low speed.
The better option is to fit and unloading valve directly off the pump outlet. When unloaded half the flow could pass through the unloading valve and half through the control valve. When the engine speed is reduced to 1000rpm the unloading valve can be closed allowing the reduced flow to pass to the control valve and operate the winch at the correct speed.
When driving pumps using engines especially with fixed displacement pumps you should always consider the working and the maximum rpm of the pump. It might be necessary to adjust the specification to cater for the extra flow.
Attributed to: Omar Khayam, 13th century philosopher
He who knows not, and knows not that he knows not, is a fool. Shun him.
He who knows not, and knows that he knows not, is a child. Teach him.
He who knows, and knows not that he knows, is asleep. Wake him.
He who knows, and knows that he knows, is a leader. Follow him.
Very best
Bob Jackson (The Hydraulic man)
More hydraulics at www.hydraulicbrain.com
Showing posts with label Hydraulic design. Show all posts
Showing posts with label Hydraulic design. Show all posts
Saturday, 31 March 2012
Sunday, 19 February 2012
Hydraulic design is like a day's fishing
When I was a small boy, nothing was more exciting than going for a day’s fishing. Not that I can remember catching much but it was the anticipation that it might just be the day when I would catch a whopper!
Many years later I now see how the experts do it and it is hardly surprising I caught very little. As a child I used the same method of fishing regardless of the conditions, location or the type of quarry I hoped to land. Top fishermen plan their task and select the right equipment to suit the conditions.
If they get it wrong, at best they will catch very little and at worse loose or break their equipment because the fish was too large for the tackle they selected for the task.
Now let us consider the Hydraulic designer, he must also consider the task. What are the loads and speeds required? Where will the equipment be used, (hot, cold, wet or dirty) and from a basket of pumps, valves, actuators and controls, select the right parts for the best result. Get the selection wrong, at best will not achieve the task and at worse cause significant damage to your customers equipment. Get it right and it’s as satisfying as catching the Whopper!
Good fishing.
Bob
More Hydraulics at www.hydraulicbrain.com
Many years later I now see how the experts do it and it is hardly surprising I caught very little. As a child I used the same method of fishing regardless of the conditions, location or the type of quarry I hoped to land. Top fishermen plan their task and select the right equipment to suit the conditions.
If they get it wrong, at best they will catch very little and at worse loose or break their equipment because the fish was too large for the tackle they selected for the task.
Now let us consider the Hydraulic designer, he must also consider the task. What are the loads and speeds required? Where will the equipment be used, (hot, cold, wet or dirty) and from a basket of pumps, valves, actuators and controls, select the right parts for the best result. Get the selection wrong, at best will not achieve the task and at worse cause significant damage to your customers equipment. Get it right and it’s as satisfying as catching the Whopper!
Good fishing.
Bob
More Hydraulics at www.hydraulicbrain.com
Saturday, 11 February 2012
Hydraulic pump suction strainers
I return to an old subject, should we fit pump suction strainers?
I posed this question to my Linked in forum (Hydraulic help) and the overwhelming opinion was to leave them off.
For those just starting out in hydraulics let me briefly recap on the purpose of suction strainers.
As its name implies this is not a typical filter but simply a piece of 125micron metal gauze rolled into a tube that fits to the end of the pump suction pipe. Particles over 125 micron will be blocked thus preventing them entering the pump possibly causing instant destruction. This sounds very admirable and because of their low cost one would see no reason for not installing them, however there is a downside.If the suction line is restricted Hydraulic Pumps will quickly deteriate due to cavitation.
Suction strainers can be difficult to change and most often end users are totally unaware that they even exist. Over time this will result in the gauze silting up and blocking the oil flow to the pump and may even collapse the strainer with catastrophic results.
Many engineers say that if the tank is very clean and free of all weld splatter, the strainer will serve little purpose. This strategy however is not risk free because you must be 100% sure that there is no way that any contaminant can drop into the tank, that the paint inside will not flake or peel and that hoses and pipework have been thoroughly cleaned prior to start up.
My opinion is, look at the application and risk assess the environment, housekeeping abilities and responsibilities of the user and the implications of serious pump failure with the consequence of serious contamination throughout the system and potential downtime to the plant. Also talk to your customer about these issues.
keep safe
Bob Jackson
More hydraulics on www.hydraulicbrain.com
I posed this question to my Linked in forum (Hydraulic help) and the overwhelming opinion was to leave them off.
For those just starting out in hydraulics let me briefly recap on the purpose of suction strainers.
As its name implies this is not a typical filter but simply a piece of 125micron metal gauze rolled into a tube that fits to the end of the pump suction pipe. Particles over 125 micron will be blocked thus preventing them entering the pump possibly causing instant destruction. This sounds very admirable and because of their low cost one would see no reason for not installing them, however there is a downside.If the suction line is restricted Hydraulic Pumps will quickly deteriate due to cavitation.
Suction strainers can be difficult to change and most often end users are totally unaware that they even exist. Over time this will result in the gauze silting up and blocking the oil flow to the pump and may even collapse the strainer with catastrophic results.
Many engineers say that if the tank is very clean and free of all weld splatter, the strainer will serve little purpose. This strategy however is not risk free because you must be 100% sure that there is no way that any contaminant can drop into the tank, that the paint inside will not flake or peel and that hoses and pipework have been thoroughly cleaned prior to start up.
My opinion is, look at the application and risk assess the environment, housekeeping abilities and responsibilities of the user and the implications of serious pump failure with the consequence of serious contamination throughout the system and potential downtime to the plant. Also talk to your customer about these issues.
keep safe
Bob Jackson
More hydraulics on www.hydraulicbrain.com
Sunday, 29 January 2012
Hydraulic Hose Burst Valves
Hydraulic Hose Burst Valves
I have talked many times about my dislike for Hose Burst valves (velocity fuse).
A cheap and nasty little valve that screws directly into the cylinder port and should close when the velocity across the valve exceeds the spring setting.
So why do I hate this valve so much?
Many unwitting users do not realise that these valves must be properly adjusted using feeler gauges if they have any chance of them working properly. The manufacturer should supply a chart with the valve showing a valve gap dimension based on flow. This is not the flow of the pump but the flow that will pass from the cylinder under normal conditions and is calculated using the displacement volume of the ram and its velocity.
The valve will not compensate for any change in temperature or load and can often close when operating under normal conditions, causing annoying stoppages. However the main purpose is that they must close should a pipe or hose burst. If the worst happens and the valve does not close, the result can be catastrophic and cause serious damage or injury.
If you are serious about protecting against hose burst then spend a little more money and do the job properly using a Pilot Operated Check valve. It will react instantly and must be built in as part of the cylinder with no pipe between the cylinder port and valve except for the pilot. This is a better quality valve and much more reliable.
Always keep in mind that there is NO complete failsafe way of hydraulically holding up any load with a ram except by using mechanical locking. Even if a new installation initially holds well, time and wear will eventually increase leakage and the load will creep down.
Be safe.
Bob Jackson (The Hydraulicman)
More stuff visit www.hydraulicbrain.com
I have talked many times about my dislike for Hose Burst valves (velocity fuse).
A cheap and nasty little valve that screws directly into the cylinder port and should close when the velocity across the valve exceeds the spring setting.
So why do I hate this valve so much?
Many unwitting users do not realise that these valves must be properly adjusted using feeler gauges if they have any chance of them working properly. The manufacturer should supply a chart with the valve showing a valve gap dimension based on flow. This is not the flow of the pump but the flow that will pass from the cylinder under normal conditions and is calculated using the displacement volume of the ram and its velocity.
The valve will not compensate for any change in temperature or load and can often close when operating under normal conditions, causing annoying stoppages. However the main purpose is that they must close should a pipe or hose burst. If the worst happens and the valve does not close, the result can be catastrophic and cause serious damage or injury.
If you are serious about protecting against hose burst then spend a little more money and do the job properly using a Pilot Operated Check valve. It will react instantly and must be built in as part of the cylinder with no pipe between the cylinder port and valve except for the pilot. This is a better quality valve and much more reliable.
Always keep in mind that there is NO complete failsafe way of hydraulically holding up any load with a ram except by using mechanical locking. Even if a new installation initially holds well, time and wear will eventually increase leakage and the load will creep down.
Be safe.
Bob Jackson (The Hydraulicman)
More stuff visit www.hydraulicbrain.com
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
Saturday, 8 October 2011
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
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
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
Subscribe to:
Posts (Atom)