Cyclic pressure tester

Orn · May 9, 2005

I have an application where I have to constantly change the pressure on four Filter body housings 1/2 gal each.

The housings are purged of air and have to be pressurized as follows

From 7.5 to 159 psi in 1 sec +/- 0.1 sec
Stay at 159 +/- 1psi for 1.5 sec
De pressurize to 7.5 psi (as fast as possible)
Stay at 7.5 psi for 1.0 sec +/- 0.1 sec

Repeat 200 000 times

This completes 1 test

The current rig is based on mechanical regulators (see attachment) solenoids and PLC for timing the solenoids.

The current system lacks accuracy and repeatability

I have been asked to redesign and build a new system.

The volume of water moved for each cycle is very small maybe as small as 200mL

Do you know of any Servo Valves that can be used with water?

Do you think a basic I/P Process control valve would respond fast enough?

Does using a motion controller with pressure as a feedback sound like a good idea to obtain the desired pressure profile?

Thanks,

Orn

Lancie1 · May 9, 2005

Do you know of any Servo Valves that can be used with water? [Not at the moment]

Do you think a basic I/P Process control valve would respond fast enough? [Sure, about any pressure controller would, and so would most PLC PID controller instruction.]

Does using a motion controller with pressure as a feedback sound like a good idea to obtain the desired pressure profile? [It would work, but it sounds like tremendous over-kill. If you have pressure transmitters already, and you already have a PLC, then install analog input and output modules, and use a PID instruction to control the pressure.]

Orn Jonsson · May 9, 2005

Well The pressure set point i.e. max and min are just a part of the task. A particular (slope) is desired on the pressure curve. Yep, I will try the least expensive way first, pressure x-ducer and probably an I/P type control valve. It would be nice though to have the accel / decel function of a motion controller....... to play with. So far the best price per axis that I have foud is aroud $1000 - a bit toooooo much.

Orn

ndzied1 · May 10, 2005

Orn,

Are you trying to get less than $1000 per axis with the valve and transducers? I don't think you can do it and get good control of the ramp.

We've done this type of system before but not on the cheap. The system folloed a UL test spec. for refrigeration valves. In this case, the # of cycles was also 200,000 but the hold time at pressure was only 0.1 sec.

We used a servo/proportional valve with a Rexroth DMX card and precision pressure transducer. The medium was oil.

You might be interested in this thread which deals with the relationship of pressure and volume:
http://patchn.com/forum1/viewtopic.php?t=612

leitmotif · May 10, 2005

Test parameters

Orn said:
I have an application where I have to constantly change the pressure on four Filter body housings 1/2 gal each.

The housings are purged of air and have to be pressurized as follows

From 7.5 to 159 psi in 1 sec +/- 0.1 sec
Stay at 159 +/- 1psi for 1.5 sec
De pressurize to 7.5 psi (as fast as possible)
Stay at 7.5 psi for 1.0 sec +/- 0.1 sec

Repeat 200 000 times

This completes 1 test

The current rig is based on mechanical regulators (see attachment) solenoids and PLC for timing the solenoids.

The current system lacks accuracy and repeatability

I have been asked to redesign and build a new system.

The volume of water moved for each cycle is very small maybe as small as 200mL

Do you know of any Servo Valves that can be used with water?

Do you think a basic I/P Process control valve would respond fast enough?

Does using a motion controller with pressure as a feedback sound like a good idea to obtain the desired pressure profile?

Thanks,

Orn

Orn

If system is purged of air and you are using water then it seems to me system is full of water and I wonder how can you pump 200 mL of water -- uhhhh how big (volume are these filters?)

If system is full of water AND you have budget constraint
pressurize the water with compressed air with a SMALL air chamber (short pipe nipple ??) at 160 psi or maybe a little higher. Use solenoid valve controlled by 159 psi switch and a needle valve to control ramp up. Depressurize by opening another solenoid controlled by pressure switch set at 7.5.

Dan Bentler

Orn Jonsson · May 10, 2005

Filters are 1.5 L each = 6L 1.5gal. Housing material is poly pro and belief me it expands under pressure

leitmotif · May 10, 2005

Ahhh plastic filters - that accounts for change in volume. Should have thought of that Orn. I think that throws compressed air out -- too shaky and dangerous at that pressure especially with plastic. Back to pumping water.

Dan

ndzied1 · May 10, 2005

Forgot to mention that the valves were piped together and tested all at the same time off one valve.

fluidpower1 · May 10, 2005

How about a Diaphragm with water on one side piped to the test and oil on the other side from a servo or proportional valve. This makes a solid system that can be controlled at a fast rate with transducers as the feedback.

Just a thought

Rod · May 10, 2005

I like Fluidpowers idea, except.
You need to move 6 gals of water - BIG diaphragm. And what happens when a bowl bursts and over pressures the diaphragm?

Back to leimotif.
Air over pneumatics in an accumulator. Preset airtank to 159PSI and just bang the air in and then vent/release the air.
shouldn't that do what you want?

My 1.5 cents worth

Rod

Orn Jonsson · May 10, 2005

Unfortunately the filter bodies are pressurized from one end then that end is shut off for 1.5 sec. and at the end of 1.5 sec the pressurized water is relieved out a different end via a solenoid valve.
It would be excellent if we could pressurize and depressurizeall from the same port. However the "German" customer has been very specific on pressurizing at the water inlet and depressurizing at water outlet ports. Why? I have not the slightest idea. It just makes things more complicated.
I like the hydro over water idea though.....

Thanks for your continuing comments.

I will try to get a hold of an accumulator, transducer and a I/P air-to-air process control valve and run some tests.
Still don't have but one source for the control valve - Burkert.

Cyclic pressure tester

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