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Vent and Drain in Custody Meter

Vent and Drain in Custody Meter

Vent and Drain in Custody Meter

Hi Engineers, I want to ask. Are PRV + vents and drains actually needed in the Custody meter stream? Or does it serve its purpose only during maintenance?

RE: Vent and Drain in Custody Meter

PRV or TRV will prevent overpressure when isolated
Vents and drains allow you to fill it and drain it when required.

I don't really understand what the question is here?

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

RE: Vent and Drain in Custody Meter

@LittleInch thank you for your response. When I'm looking at custody meter P&ID/GA drawing, either for gas or HC liquid, some stream configuration has vent or drain after strainer or gas filter but some other dont have it installed to the metering stream even after the branch to the proover. That's makes me wonder, is it mandatory or depends on something to add vent/drain in metering system? or it's just me who overthink it? Because unnecessary branch just adds more uncertainity to meter calculation.

RE: Vent and Drain in Custody Meter

Depends on each system and where the isolation valves are etc.

The metering element is normally only part of the whole thing and you don't touch that bit, i.e. the 10D up and downstream or whatever.

Every thing else is dependant on the particular fluid, temperatures, configuration and to a certain extent the designer.

Some stick vents and drains EVERYWHERE, others only where you really need them.

Gas lines in particular can get away with no PRV, but liquid lines often have a TRV to avoid solar gain pressure rise.
There again some places have TRVs all over the place, some limit them depending on volume (never understood that tbh), should be any locked in section IMHO.

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

RE: Vent and Drain in Custody Meter

I see, thank you again for your answer. Now I have better idea wether to add them or not. I would let people knows that I'm still open for their answer and experience. More story means better insight.

RE: Vent and Drain in Custody Meter

When you clean a basket strainer, you can trap air in it when it is being closed. If the strainer is large, it could be better to vent and purge the air out of it rather than allowing that air to carry into the meter and the downstream piping. It could also be helpful to have a drain in case a liquid meter requires maintenance, or if a gas stream is not entirely dry.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

RE: Vent and Drain in Custody Meter

Vents and drains are only for maintenance routines and also for operational (offline) meter proving operations, not for normal operation

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