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
Wednesday 30 March 2011
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?
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