Valve Fatigue Testing 2

[MarkXX]

Hello,

I am trying to devise a system in which I can cycle a small check valve using a water at a high frequency (20-50Hz). The problem is that I would like a closed system and be able to supply a back pressure to the closed valve up to 35 psi while allowing the fluid to circulate to the upstream side of the valve which will be temporarly at a lower pressure. The system will be displacement driven by use of a piston.

Essentially what I want to do is this:

push fluid through the valve using a bellow or piston, after valve is closed apply a pressure to the downstream side of the valve of 35 psi (delta P = 35 psi), move the fluid that past through the valve back to the upstream side of the valve to be pushed through again. Do it at 20-50 Hz. The valve size would be between 2 to 3 cm.

I have some ideas but they involve complicated controls. I would imagine that this has been done already. Any help is greaty appreciated.

Also, does anyone have any idea or links to how valve companies fatigue test their valves? That might help.

Thank You. Have a great day.

 

[gerhardl]

I have no idea how this is tested (if at all). But anyway a suggestion:

a) Two equal checkvalves in parallell in two separate pipelines, pipeline started in open Y form after the piston, valves mounted for stopping opposite ways, pipeline then connected to downstream resrvoir.

Stroke forward of piston: filling downstream reservoir, through one checkvalve, stroke backwards suction back to piston chamber through the other. Downstream chamber may be regulated in pressure by air or gas filled rubber balloon inside chamber. Downstream chamber with or without extension and arrangement as upstream as suitable.

b) Variation of above but with checkvalve in one pipeline and overflow valve back to piston chamber.

Note: For b solution 'waterhammer' pressure peaks may cause the overflow valve to open, and your circuit should include protection for this in best possible way, several ways possible.

 

[vpl]

Why do you need to do this? Knowing your application might help us give better advice.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[JimCasey]

If you start cycling the valve that fast you will build up a continuous flowrate. You just can't stop water that quickly.

I envision a mechanism almost exactly like an air compressor, where on the downstroke a check valve lets fluid into the cylinder, and on the upstroke that check valve closes and another check valve lets fluid OUT of the cylinder. However at 30 hz the water will likely continue to flow in even during the upstroke. Your check valves will flutter but the actual closing will be only as necessary when the flowrate decays. Still, it will be a lot of hammering and wear on the check valve an you are highly likely to gather a lot of fragments that were formerly part of a check valve assembly. Make sure you protect the cylinder with a strainer.