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
Sunday, 29 January 2012
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
Tuesday, 27 December 2011
Sunday, 18 December 2011
Hydraulic Safety
Hydraulic Safety
Anyone involved with Hydraulic equipment can be subjected to considerable risk unless good working practice is always adopted. Hydraulic machines are often very powerful with large dynamic forces and high pressure fluid that can also sometimes be scalding hot.
When working on hydraulic equipment it is a good idea to do an assessment of risk (download example from www.hydraulicbrain.com)
Never work on systems until you are sure that the pump is switched off and all suspended loads are lowered so nothing can fall or move should you remove pipe-work.Accumulators are a source of large potential energy so ensure they are completely discharged.
Prevent equipment being started up by third parties. Maybe you can lock the system,remove the key,electricalfuses and put up signs to say that the system is being worked on and must not be used
There are many dangers for the Engineer and many things that you can do to make yourself safe.
For more stuff on Hydraulic Safety log on to www.hydraulicbrain.com
Very best
Bob
Anyone involved with Hydraulic equipment can be subjected to considerable risk unless good working practice is always adopted. Hydraulic machines are often very powerful with large dynamic forces and high pressure fluid that can also sometimes be scalding hot.
When working on hydraulic equipment it is a good idea to do an assessment of risk (download example from www.hydraulicbrain.com)
Never work on systems until you are sure that the pump is switched off and all suspended loads are lowered so nothing can fall or move should you remove pipe-work.Accumulators are a source of large potential energy so ensure they are completely discharged.
Prevent equipment being started up by third parties. Maybe you can lock the system,remove the key,electricalfuses and put up signs to say that the system is being worked on and must not be used
There are many dangers for the Engineer and many things that you can do to make yourself safe.
For more stuff on Hydraulic Safety log on to www.hydraulicbrain.com
Very best
Bob
Sunday, 6 November 2011
The Counterbalance valve
The counterbalance valve is used for load holding and prevents the load running away uncontrolled. The valve automatically throttles the outgoing flow using a pilot signal from the input flow leg to the ram or motor. The valve symbol is very similar to the Relief valve with a normally closed function and a check valve looped around the main valve.
To open the valve it will need a pilot pressure and for very large loads this should be as small as possible where lighter loads should be higher. The valve will be made with a designed pilot ratio, this is ratio of the pilot pressure against the induced load pressure to open the valve and can be typically 3:1 to 10:1
To establish the way to set up the Counterbalance valve you must know the Pilot Ratio. Pilot Pressure= Valve Setting Pressure – Pressure induced by load divided by the Pressure Ratio + the ratio of piston area divided by the annular ram . A hydraulic motor would be 1.
If we are using a hydraulic motor on a winch it will be important to ensure that there is enough pressure to release the brake. This might require a low Pressure Ratio to achieve enough pressure to release the brake.
If you do not set these valves up correctly the system can become unstable, the ram or motor may not move and in the case of winches the brake might not release.
For more about load holding become a member of www.hydraulicbrain.com
Very best wishes
Bob
To open the valve it will need a pilot pressure and for very large loads this should be as small as possible where lighter loads should be higher. The valve will be made with a designed pilot ratio, this is ratio of the pilot pressure against the induced load pressure to open the valve and can be typically 3:1 to 10:1
To establish the way to set up the Counterbalance valve you must know the Pilot Ratio. Pilot Pressure= Valve Setting Pressure – Pressure induced by load divided by the Pressure Ratio + the ratio of piston area divided by the annular ram . A hydraulic motor would be 1.
If we are using a hydraulic motor on a winch it will be important to ensure that there is enough pressure to release the brake. This might require a low Pressure Ratio to achieve enough pressure to release the brake.
If you do not set these valves up correctly the system can become unstable, the ram or motor may not move and in the case of winches the brake might not release.
For more about load holding become a member of www.hydraulicbrain.com
Very best wishes
Bob
Saturday, 29 October 2011
What is maximum pressure?
These days we expect hydraulic pumps should be fully supported with detailed technical information ensuring that we use the pump in the correct application.
Often we have pages of stuff showing everything from displacement to recommended oil type.
I often find that the pressure duty is not well defined like what pressure can I safely generate without the pump falling apart. You will read descriptions like continuous, intermittent and peak.
Continuous speaks for itself but what about intermittent and peak, what does this description really mean.
Many years ago when I sold hydraulic components for a well known manufacturer the pumps had different ratings for industrial than mobile. For what I can only imagine were commercial reasons, the mobile pump pressures were much higher.
I have also used some pumps well outside their recommended pressure ranges (only for specific applications) and although not a practice I recommend I do wonder what technical basis manufacturers use to determine their pump pressure ratings.
I would like to see a graph with a direct correlation between pressure and life. I want to know that if I design a system that runs once a month for 15minutes at higher than normal pressure should I need to spend much more money on a more expensive pump.
Surely we should be able to get a better idea of pump life without always having to buy the highest spec pump or face the possibility of a bucket of scrap metal after just a few cycles.
Very best
Bob
Often we have pages of stuff showing everything from displacement to recommended oil type.
I often find that the pressure duty is not well defined like what pressure can I safely generate without the pump falling apart. You will read descriptions like continuous, intermittent and peak.
Continuous speaks for itself but what about intermittent and peak, what does this description really mean.
Many years ago when I sold hydraulic components for a well known manufacturer the pumps had different ratings for industrial than mobile. For what I can only imagine were commercial reasons, the mobile pump pressures were much higher.
I have also used some pumps well outside their recommended pressure ranges (only for specific applications) and although not a practice I recommend I do wonder what technical basis manufacturers use to determine their pump pressure ratings.
I would like to see a graph with a direct correlation between pressure and life. I want to know that if I design a system that runs once a month for 15minutes at higher than normal pressure should I need to spend much more money on a more expensive pump.
Surely we should be able to get a better idea of pump life without always having to buy the highest spec pump or face the possibility of a bucket of scrap metal after just a few cycles.
Very best
Bob
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