Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
(OP)
Unless I am wrong, isn't the design pressure of piping downstream of an isolation valve that is capped with a pressure gauge, supposed to be equal to the upstream design pressure? And I believe this to be case also even if there are two isolation valves that are normally closed; since valves cannot be guaranteed to be 100% leak tight. By this virtue, the pressure gauge's design pressure should equal the upstream (of the valves) design pressure.
Any feedback or opinion is welcome, please.
Any feedback or opinion is welcome, please.





RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
What is the purpose of pressure gauge that is located after a closed isolation valve?
Dejan IVANOVIC
Process Engineer, MSChE
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
Also, I don't see the purpose of pressure gauge with a "Normally Closed" valve upstream of it - unless this drawing refers to flushing/blowing procedure or similar.
Dejan IVANOVIC
Process Engineer, MSChE
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
If through leakage of valves is cause for concern, a block and bleed or double block and bleed may be required for isolation. In some other cases, a single check valve may suffice. It depends on the hazard.
If, however, a piece of instrumentation such as a pressure gauge may be damaged, or worse still, potentially rupture with injury, merely as a result of the misoperation of a single hand valve (a highly probable event), most designers would find the resulting risk to be unacceptable and would require a means to mitigate that hazard.
Let's say, for instance, that a line may be at high pressure during some operations, but may require accurate measurement of a lower pressure during a separate operation or step. There are a number of ways to do this safely. One is to specify a pressure transmitter rather than a pressure gauge, which has sufficient overpressure handling capacity to survive misoperation of its block valve. Another would be the removal of the instrument during high pressure operation. Another would be the installation of a protection device such as a relief valve or rupture disc. Yet another might be physical, electrical or pneumatic interlocking which prevents the valve from being misoperated. Which of these measures is best for the particular situation requires a basic hazard identification exercise based on the specifics of the application.
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
Looks like the PI/PG in question is only used on certain occasion to confirm low or no pressure in a system normally with a much higher pressure. In that case the PI/PG really should have a snubber or pressure limiting valve in front of it to avoid over pressurising the gauge accidentally. Also then needs a vent valve to release this pressure at some point on the PI line.
he key lies in the purpose behind this instrument.
you could always use a PT with a display where the body of the PT is rated to full U/S line pressure, but the element inside is ranged for a much smaller span. If you over pressure the PT, I don't think it likes it very much, but it won't break.
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RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge
Double block and bleed with cavity drain might work.
RE: Design pressure of piping downstream of an isolation valve that is capped with a pressure gauge