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# Operation of a pressure control valve if reverse flow is expected

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## Operation of a pressure control valve if reverse flow is expected

(OP)
Say we have a pressure control valve which is designed to control the upstream pressure in a line at a certain value say 5 bar. Flow is normally from left to right and the upstream pressure is normally higher than the downstream pressure. Now if the downstream pressure becomes higher than the upstream pressure such that the flow is reversed (ie. from right to left), what is the pressure control valve supposed to do? Does it switch to a downstream controller? Or does it block reverse flow? Or does it just stay fully open?

### RE: Operation of a pressure control valve if reverse flow is expected

Depends on how it is controlled. Sounds to me like a back pressure control where the valve closes when pressure falls below 5 bar and opens when it is above 5 bar? So all depends what happens to the u/s pressure when you get back flow. If it goes anyone 5 bar then it will just continue to open.

Does depends on type of valve. Some don't like reverse flow and can fail or jam in reverse flow mode. Normally you put two nrvs, one to prevent flow through the valve and the second to allow bypass flow if that's what you want.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Operation of a pressure control valve if reverse flow is expected

If a pressure control loop measures a higher pressure than the set-point then it should close the valve. If upstream pressure drops sufficiently so that downstream pressure is higher than upstream pressure - but still at or below set point (downstream) then the loop will keep the valve open unless you have some other measures to prevent this. A globe valve will have a flow direction and will have a tendency to close if the flow is reversed, but the actuator could keep it open anyway (actually flow to open or flow to close is something that you can specify).

Best regards, Morten

### RE: Operation of a pressure control valve if reverse flow is expected

It may depend on the control scheme of the system. With the pressure instruments designed at both upstream and downstream, the control valve may be set to open if the upstream pressure is higher, and close as the pressure reversed.

### RE: Operation of a pressure control valve if reverse flow is expected

usually there is a check valve or one way valve if back flow not wanted prevent back flow , then low flow will occur followed by high pressure in the line safety valve it could open ...,should be another device such Blow off valve or bypass valve where to release the excess pressure .

### RE: Operation of a pressure control valve if reverse flow is expected

Missing information here from Adack, seems that this is question about an existing loop.

What is the purpose of the question?
If general it is already answered, if a question of help with layout or designed more details are needed.

### RE: Operation of a pressure control valve if reverse flow is expected

normal operation:upstream pressure increases,control valve opens (dumps the pressure)
the pressure measurement only sees pressure,the valve operation only does what it is designed to do
so if pressure rises as a result of pressure rise downstream, the valve opens

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