Control valve actuator - spring and diaphragm Vs spring return piston

Hi all,

A customer wants to buy control valves.
Shutoff pressure is 130 barg.
Each vendor is justifying his position, one says S&D is fine, another says piston spring return.
Valve sizes from 4" to 8" rated 900# and above.

I felt because of high shutoff pressure piston with spring would be a better selection, because of the higher out put from it. Also it can be used for high shutoff pressures without any issues.

Your suggestions would be helpful to come to a decision.
Cheers
Jack

 

[Compositepro]

An actuator applies force not pressure. Pistons and diaphragms can both supply the same force but a diaphragm actuator usually uses lower pressure air on a larger area diaphragm than a piston. With spring return, it will be the spring that is the limiting factor and you cannot fit as large a spring on a small piston as you can with a larger diaphragm. I started my career in a chemical plant built in the 40's that was all pneumatically controlled using 3-15 psi control signals that directly operated diaphragm type control valves. The controllers were basic pneumatic computers. It was an amazingly robust and elegant system.

 

[JackGardener]

Hi Compositepro,
Thanks for your reply, but can we achieve class V shutoff at that high pressure with S&D actuator.
Some colleagues say the pounds per linear square inch for this case will be very high and S&D actuator may not achieve the seat tightness.

Thanks
Jack

 

[Compositepro]

Only the valve manufacturer can reliably answer your question. But there is no reason that piston or diaphragm is relevant. Also, most large, high-pressure valves should be pressure balanced so that system pressure does not affect the force required to operate the valve.