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
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