pilot operated psv 1

[qndp77]

A pilot operated psv with sensing lines to the pilot.

Lets say situation is operating at normal operating pressure.
Will isolating the pilot sensing line cause the main psv to lift because there is no pressure on the psv dome? Does this even happen at very low pressure as well?

Is there a circumstance that isolating the sensing line will not cause the main psv to lift?

 

[The Obturator]

If there is no pressure on the main valve dome, as you have stated, then the main valve will open.

If you rather mean will the main valve open if there is pressure trapped in the valve dome, then theoretically no.

If the sensing line is damaged such as by being crimped, then there will always be a small amount of pressurised fluid flowing to the pilot. Ultimately, for any pressure trapped in the dome, the main valve disc will overcome this pressure and open to a degree. Some manufacturers will tell you that it could be within 10% of set pressure (not overpressure).

Perhaps a better scenario is, will the main valve open if the pilot has failed to open at set pressure.

Are you looking to prevent main valve opening for any reason? (eg. hydro test of vessel). At low pressure the main valve can leak as the full pressure is not above the main valve disc keeping the main valve closed. There are options available to gag the main valve differing by manufacturer.

Per ISO, only the term Safety Valve is used regardless of application or design.

 

[LittleInch]

But when you isolate it you lock in the pressure.

If this is liquid then even a small temperature rise could cause it to lift.

But no pressure wouldn't lift the main valve.
Different pilots work in slightly different ways so make sure you know what your particular pilot does.

If your sensing line doesn't change in pressure due to temperature or leakage then isolating the sensing line basically means the main PSV won't lift even in circumstances when it should.

It is no different to simply isolating the relief valve.

Normally these are locked open valves to prevent people from isolating your safety device.

Why on earth do you want to do this???

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

 

[Sabeau]

Are you trying to maintain the main valve at the closed position even when the upstream pressure is low such as before a compressor startup or similar?

 

[gguliye]

Obturator,
Do we have gags for POPRV? I haven't seen it I have seen it only for spring operated relief valve.
Regarding the question:
I would like to add the following point. As far as I am aware of, some manufacturers put spring on the piston for transportation and to dampen (to prevent up to some degree) the initial opening of the piston due to the low pressure trapped in dome.

 

[Sabeau]

gguliye,

Yes, POPRVs can also have gags.

You are correct, there is often a spring in the dome of the main valve, however, these are typically very very low rate as they would otherwise impact the performance of the valve.

 

[The Obturator]

We're diverging from the original question now.
Not all manufacturers Pilot Operated Pressure Relief Valves can be gagged. Depends on the design. You need to refer their catalogues.
Main valve spring is purely there as a "return spring" and not for set pressure. Some manufacturers in the past did not even usa a spring for large sizes since weight/gravity was sufficient.

Per ISO, only the term Safety Valve is used regardless of application or design.