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
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