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Non-Flowing Pilot Operated PSVs

Non-Flowing Pilot Operated PSVs

Non-Flowing Pilot Operated PSVs

Dear All,

As we all know, pilot operated are recommended by PAI 520 PI for two phase application as they excellently withstand the variation in backpressure which can reach up to 70% of the PSV set pressure. There is a sub-category of the Pilot operated valves which is called non-flowing type and is equipped with a blowdown seat which closed when the Pilot lifts to open the PSV and prevents the circulation of the fluid inside the pilot.
In typical industry standards, such non-flowing type is recommended in services which are unclean such as production fluids. despite that generally pilot operated valves are known to be strictly suitable for clean services.

In your views, non-flowing pilot operated functionality allows it to be used for such unclean services such as when containing asphaltene or wax?



RE: Non-Flowing Pilot Operated PSVs

Asphalt and wax like fluids are definitely not recommended for pilot operated Pressure-relief Valve applications regardless of design. The pilot has very small and intricate chambers and passages that would encourage a blockage from these type of fluids.

At best, if you need to use a POPRV, then talk to one of the manufacturers that have designs shielding the protected fluid from entering the pilot

Depending on fluid viscosity etc., you may also need to consider a jacketed / heat traced inlet to maintain the fluid in a more manageable liquid state for the PRV to open properly. I would be looking at a steam jacketed spring operated PRV with accessories such as purge cleaning aimed at the nozzle area.

Note that most POPRV designs are now non flowing. Early POPRV designs were originally flowing type and used on modulating type POPRV's.

Nowhere does it say that POPRV's are preferred for multi phase fluids. Depending on manufacturer and design, spring operated PRV's can also attain high back pressures. 50% is the published API figure but not necessarily the limitation.

Note also that there is a separate safety/relief valve forum for these questions.

*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

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