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 faults. Show all posts
Showing posts with label hydraulic faults. Show all posts
Saturday, 31 March 2012
Tuesday, 20 March 2012
What is the difference between airation and cavitation?
Often miss diagnosed and not surprising because the symptoms are similar but with very different causes.
Airation
Very simply this is the result of air getting into the hydraulic fluid and most likely through the suction pipe or if the oil level has been allowed to get too low, partially uncovering the inlet to the pump. The pump will sound noisy (lumpy), a very similar noise to cavitation and undesirable for the following reasons.
1) The system becomes spongy and movements become erratic with pressure fluctuations.
2) The lubrication of the sliding parts within the pump etc will be reduced and lead to failure.
3) Dieseling effect could cause ignition with very high temperature spots, damaging seals
The Cure: The suction pipe will be subject to vacuum so do not expect to see any oil leak so best check all fittings between the strainer and pump inlet. Another way is a little messy but try grease or oil around the joints and listen for pump tone change.
Cavitation There are many reasons for cavitation but they all result in restricting oil entering the pump.
Best to start with easy stuff first:
1) Tank breather blocked (remove and replace)
2) Suction valve not fully open
3) Oil cold or too thick (check viscosity)
4) Suction Strainer clogged (remove and replace)
5) Suction pipe too small
6) Suction pipe too long
7) Pump speed too high
Cavitation is very destructive and will damage the pump in a very short time. Minute explosions take place on the surface of the metal during the transition from vacuum to high pressure with temperatures reaching greater than that on the sun. Pitting and metal removal will quickly lead to failure.
Hope you find this interesting and helpful and you can find more valuable information if you sign up at www.hydraulicbrain.com
Keep safe
Bob Jackson (The Hydraulic man)
Airation
Very simply this is the result of air getting into the hydraulic fluid and most likely through the suction pipe or if the oil level has been allowed to get too low, partially uncovering the inlet to the pump. The pump will sound noisy (lumpy), a very similar noise to cavitation and undesirable for the following reasons.
1) The system becomes spongy and movements become erratic with pressure fluctuations.
2) The lubrication of the sliding parts within the pump etc will be reduced and lead to failure.
3) Dieseling effect could cause ignition with very high temperature spots, damaging seals
The Cure: The suction pipe will be subject to vacuum so do not expect to see any oil leak so best check all fittings between the strainer and pump inlet. Another way is a little messy but try grease or oil around the joints and listen for pump tone change.
Cavitation There are many reasons for cavitation but they all result in restricting oil entering the pump.
Best to start with easy stuff first:
1) Tank breather blocked (remove and replace)
2) Suction valve not fully open
3) Oil cold or too thick (check viscosity)
4) Suction Strainer clogged (remove and replace)
5) Suction pipe too small
6) Suction pipe too long
7) Pump speed too high
Cavitation is very destructive and will damage the pump in a very short time. Minute explosions take place on the surface of the metal during the transition from vacuum to high pressure with temperatures reaching greater than that on the sun. Pitting and metal removal will quickly lead to failure.
Hope you find this interesting and helpful and you can find more valuable information if you sign up at www.hydraulicbrain.com
Keep safe
Bob Jackson (The Hydraulic man)
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
Tuesday, 17 January 2012
Oil Viscosity
Viscosity of Hydraulic oil
Often in hydraulic systems the type of oil can be the last thing to consider in the overall design.
ISO 32 mineral oil is the most common Hydraulic oil and I often advise my clients to use this grade of oil because of its availability and compatibility with most pumps, valves and hydraulic components.
The viscosity can be extremely important and I will give a few examples of situations that I have encountered where the oil has been a key factor to resolving problems.
1) We designed a system for an animal park. Large sliding hydraulic doors enclosed Rhinoceros and it was our job to ensure that the doors closed quickly but with minimum force so not to injure the animal. Everything worked to plan but our client complained that on some occasions the electric motor would cut out. We discovered that the motor only cut out on cold days when the oil was at its thickest. The pack worked off 240v 30amp supply and we had no way of increasing the supply. The simple solution was to change the oil from iso 46 to 32. Our customer never had another failure and was very pleased with the simple remedy.
2) An aluminium casting machine uses hydraulic rams to tilt the machine and allow molten metal to fill the mould. When solidified the machine is tilted back to open the die and remove the casting. We had already increased the speed by using a Regen circuit but our customer wanted even more speed. We noticed that there was a difference in speed from morning to afternoon when things began to slow down. By monitoring the temperature we knew this was due to the change in oil viscosity. We recommended he replace the iSO32 for 46 and saved 8 seconds in the total cycle time.
3) In a saw mills proportional valves were used to set adjustable fence. The customer complained that the hydraulics needed to run for at least one hour before the system cut accurately. We changed the oil to thinner grade and immediately improved the accuracy without the need to waste time to bring the oil up to temperature.
The viscosity of hydraulic oil can be very important and often a great problem solver without having to modify expensive hardware.
Always best to check with pump manufacturer to be sure that the pump or motor will not be damaged by a change in oil viscosity.
A great problem solver to keep up your sleeve!
Very best
Bob Jackson
More hydraulic stuff at www.hydraulicbrain.com
Often in hydraulic systems the type of oil can be the last thing to consider in the overall design.
ISO 32 mineral oil is the most common Hydraulic oil and I often advise my clients to use this grade of oil because of its availability and compatibility with most pumps, valves and hydraulic components.
The viscosity can be extremely important and I will give a few examples of situations that I have encountered where the oil has been a key factor to resolving problems.
1) We designed a system for an animal park. Large sliding hydraulic doors enclosed Rhinoceros and it was our job to ensure that the doors closed quickly but with minimum force so not to injure the animal. Everything worked to plan but our client complained that on some occasions the electric motor would cut out. We discovered that the motor only cut out on cold days when the oil was at its thickest. The pack worked off 240v 30amp supply and we had no way of increasing the supply. The simple solution was to change the oil from iso 46 to 32. Our customer never had another failure and was very pleased with the simple remedy.
2) An aluminium casting machine uses hydraulic rams to tilt the machine and allow molten metal to fill the mould. When solidified the machine is tilted back to open the die and remove the casting. We had already increased the speed by using a Regen circuit but our customer wanted even more speed. We noticed that there was a difference in speed from morning to afternoon when things began to slow down. By monitoring the temperature we knew this was due to the change in oil viscosity. We recommended he replace the iSO32 for 46 and saved 8 seconds in the total cycle time.
3) In a saw mills proportional valves were used to set adjustable fence. The customer complained that the hydraulics needed to run for at least one hour before the system cut accurately. We changed the oil to thinner grade and immediately improved the accuracy without the need to waste time to bring the oil up to temperature.
The viscosity of hydraulic oil can be very important and often a great problem solver without having to modify expensive hardware.
Always best to check with pump manufacturer to be sure that the pump or motor will not be damaged by a change in oil viscosity.
A great problem solver to keep up your sleeve!
Very best
Bob Jackson
More hydraulic stuff at www.hydraulicbrain.com
Monday, 2 January 2012
My Top 7 Hydraulic Faults
I am often called out to Hydraulic breakdowns that take less than 1 minute to find and fix.
This can be an embarrassment for my customer and gives me no pleasure in having to give him a substantial bill for just 60 seconds of my time.
I have listed my 7 top simple faults that could save you a small fortune as well as the costly down time of your piece of machinery.
Check out my top 7 favourite faults before you start looking for more difficult reasons for your Hydraulic problem.
Register on my site www.hydraulicbrain.com for my 7 top faults.
Very best
Bob
This can be an embarrassment for my customer and gives me no pleasure in having to give him a substantial bill for just 60 seconds of my time.
I have listed my 7 top simple faults that could save you a small fortune as well as the costly down time of your piece of machinery.
Check out my top 7 favourite faults before you start looking for more difficult reasons for your Hydraulic problem.
Register on my site www.hydraulicbrain.com for my 7 top faults.
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
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
Subscribe to:
Posts (Atom)