3 replies to this topic

[mm217]

Dear all;

I have been involved with design pressure of equipment on downstream of pumps since some years ago....I want to know if it is possible to reduce design pressure of an equipment on pump discharge line with pressure control valve?! Some body said to me if we put pressure control valve before the equipment and it is failed closed one we can put class break there and reduce design pressure of downstream equipment.
Please guide me based on your valuable experiences. Thanks a lot.

[ankur2061]

mm217,

Valve "Fail Closed" is a attribute given to the valve to fail close due to say instrument air failure or power failure. This pre-designated attribute does not account for the mechanical failure of the control valve which can also cause the valve to be "stuck open". Hence the control valve failing in the "stuck open" position is a very credible scenario. I personally would not consider valve "Fail Closed" as a design guide for providing a lower design pressure downstream of the control valve. IMO, the risk outweighs the benefits. But then, you can always do a "risk analysis" to evaluate the probability of failure (POF) in the open position and its consequences on the downstream system.

If I had to go for such a "risk analysis" study for the control valve, one important recommendation I would make is to have double valves with TSO (Tight Shut-Off) on the by-pass for the control valve.

Hope this helps.

Regards,
Ankur.

[fallah]

Some body said to me if we put pressure control valve before the equipment and it is failed closed one we can put class break there and reduce design pressure of downstream equipment.

mm217,

You cannot reduce design pressure of downstream equipment of a control valve just due to the reason that the CV is fail closed. Even a FC control valve can be in wide open position due to stucking/controller malfunction/...
In other word, you cannot take credit on a control valve for any favourable response in order to reduce its downstream design pressure.

Fallah

Edited by fallah, 10 June 2012 - 03:11 AM.

[mm217]

Dear Ankur & Fallah;

I wished I could do that but as you said it seems to be impossible. Thanks for your cooperation.