Differential pressure across valve

[awastha]

Can 80 bar differential pressure cause any problems while or after opening the valve, if WP is 345 bar? Can it damage the seats, will valve leak in future? We have limitations for depressurising across valve. If valves are 5000 psi rated then aren't they capable to handle 80 bars? How differential pressure really works and causes problems?

 

[LittleInch]

what type of valve are you talking about?

Ball valves don't like differential pressures when opening / closing. If you have this sort of demand, you will need only metal seats with no inserts or soft bits anywhere, but you then need to accept the leakage rate for metal seated ball valves.

If you have specified this as a requirement to the vendor, then specific types of seals and valves exist, normally classified as severe duty, or similar wording, but otherwise, the differential pressure is normally limited to a small fraction of the maximum isolation pressure

Other valve types fare much better.

In short, if you need to have that functionality (high dp), then allow for it otherwise the standard design of ball valve doesn't like it IMHO.


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[gerhardl]

As LittleInch point out, it all depends on type of valve, construction, fluid and operational criteria. Even pipe layout for and after the valve will influence the performance and possible cavitation at these pressures and differential pressures.

In short: the valve has to be built suitable (recognized ok by the manufacturor) for all the details mentioned above. Especially the time in partial opened/closed valve in critical positions (positions giving cavitating) is critical.

A typical simple example of misusing a valve can be a BFL or ball valve throtteled to give a water pipeline of some size (say about 600mm) a slow fill at startup. If left in almost closed position for some hours this might be OK at low pressures (4-6 bars), but could be highly damaging at higher pressures (say 12 bar and up).

Other examples are free outlet from high-pressure valves where even short pipelines after the outlet valve might create cavitational conditions back to the valve itself, again all depending on details of valve,pipeline and flow.