Gradually increasing pressure from a static source

by David
(Ohio, USA)

I work in a liquid refinery. Our air compressors run at about 100 psi. In our refinery, there are air actuated valves that snap closed when there's a problem. The quick snap of the valve closing causes liquid that was moving through the lines at 60 gallons per minute to come to a complete stop, creating a great deal of back pressure. Recently, we've had some cracks developing in the lines because of the stress of these valves closing so quickly. Is there something along the lines of a regulator that would allow the valve to gradually close over the course of say, 3 seconds, instead of pretty much instantly?

Thanks!

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Bill says...

David, I think you are describing a valve that is designed to "fail closed", and it uses a spring to accomplish this operation when the air supply that keeps the valve open is shut off, whether on purpose or by loss of system pressure.

The solution is to use a double acting valve too, but one that opens and closes using air pressure, rather a spring on the close cycle. Then, you can meter the air out of the exhaust port on the close cycle, and that will slow down the valve, reducing or eliminating liquid hammer.

The issue then, of course, is what happens if you lose all of your air in the system? The valve will not move, and it's no longer "fail close".

The solution to that is to build some redundancy into the circuit, so that in the event there is a system wide air loss, a reservoir close to the valves in question will provide enough air to close the valves that need closing.

Hope this helps. Thanks for writing in.

Cheers,

Bill