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Old June 14th, 2003, 05:55 AM   #1
Prince
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Hydrotest pressure on me !

My dear friends !

I hate the high pressure and I always tried to get out of that but now I am inside and there is no way out !

I am negotiating for a 350 bar pressure test machine for the pipes. Don't advice me not to touch this ****, I am in it to the neck and It is very hard to tell you why I can not get out of it !

Hydraulically speaking my normal experience with pressure is including the very ordinary lubrication units 4 bar and normal hydraulic units for the cylinders (not over 100 bar). I have worked with pressure control automatin of course. but not this high !

As always I accepted the thing that I did not know ! the problem worsen when I realized that the mechanicals even don't know nothing about the fact !

The real problem is this :

They fill the pipe with water and then they start adding pressure with a high pressure pump to 5000 psi , the pipe is fastened one side with a ram cylinder which must stand the pressure so I must synchronize the pressure of water inside the pipe and the oil for the ram. besides I must consider the leakage of the oil from the seals and also the valves. I am using siemens so I must go to the multiloop ratio control of PID control and try to synchronize two pressures.

Now here is the problem:

I know enough to know that There are a lot of things that I don't know about this machine . I wondered if anybody have an experience with a hydrotester like this or any simillar device who can advice me about.I want to know more about the proportional valves and pressure switches in high pressure.Any comment form the experienced guys would be a great help.

Please Please Help me !
I promise that I won't start a project without the needed information , I will never enter the experienced designers vicinity again !
bawling
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Old June 14th, 2003, 06:02 PM   #2
Peter Nachtwey
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It looks like you stepped in it with both feet.

Quote:
Originally posted by Prince

I wondered if anybody have an experience with a hydrotester like this or any simillar device who can advice me about.
I am very familiar with the control on presses and hydroforming. Hydroforming is very close to what you are doing only the pipe is pressurised until it expands against a mold.

Quote:
Originally posted by Prince

I want to know more about the proportional valves and pressure switches in high pressure.Any comment form the experienced guys would be a great help.
See Industrial Fluid Power Society
There is a person on that forum that knows a lot about the components of hydraulics and hydraulic circuits. My specialty is hydraulic controls.

I know you should use a servo valve instead of a proportional valve, you should use pressure transducers with analog outpus instead of switches, and that the PLC will probably not be fast enough. There are hydraulic motion/pressure controllers that have updates faster than a millisecond with 16 bit analog inputs with 8 times over sampling. They will make the job easier.

Quote:
Originally posted by Prince

I hate the high pressure and I always tried to get out of that but now I am inside and there is no way out !
Controling 1000 psi or 10000 psi is all the same. It is the mechanical part of the hydraulics that changes.

Quote:
Originally posted by Prince

The real problem is this :
The real problem is the hydraulic/mechanical design. If that is done right then your job can be easier. Getting real hydraulic motion/pressure controller will also make things easier. But, no controller is going to compensate for a poor hydraulic/mechanical design, so that is most important.

Quote:
Originally posted by Prince

They fill the pipe with water and then they start adding pressure with a high pressure pump to 5000 psi ,
Normally an intensifier is used. This way you can use oil at about 100 bar to control the pressure at 350 bar. Controlling a pump directly is difficult because they are so slow to respond to a control signal. The slow response can be improved by adding an accumulator and a servo valve, but accumulators at 350 bar is not a good idea. Using a servo valve and accumulator at 100 bar works well.

Quote:
Originally posted by Prince

the pipe is fastened one side with a ram cylinder which must stand the pressure so I must synchronize the pressure of water inside the pipe and the oil for the ram.
Don't you mean that you only need to keep the force and the ends holding the caps on higher than the force of the water trying to blow the caps off? Can't you just apply force on the caps so that the water pressure can possibly push the caps off?

Quote:
Originally posted by Prince

besides I must consider the leakage of the oil from the seals and also the valves. I am using siemens so I must go to the multiloop ratio control of PID control and try to synchronize two pressures.
No problem with the right controller. This would be a lot of work in a PLC and even then it might not work well enough by the time you got done.

People do four corner presses all the time. In this case the four corners must be synchronized by position until they hit the material and then the pressures are ramped up together while the skew between the axes is being monitored.

Quote:
Originally posted by Prince

Please Please Help me !
I promise that I won't start a project without the needed information , I will never enter the experienced designers vicinity again !
bawling
Normally a project like this would be done by an OEM or major hydraulic company like Parker that has ( should have ) lots of experience in doing high pressure controls.

If this is a one of a kind system then there will be a lot of learning($$$) involved.

There better be some in charge that knows what he is doing.
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