PRV vs. PSV vs. PSRV 2

[heaterguy]

Please clarify when to use a PRV, a PSV and a PSRV. Is the difference application specific or code specific? Please identify (PRV, PSV and PSRV) on the following ASME pressure vessels:

Thermal relief valve on liquid containment:
Thermal relief valve on gas containment:
Fire relief valve on gas / liquid containment:

Or on an ANSI piping system for dropping from 900# to 300#:

TYIA,
HG

 

[Ashereng]

These terms are pretty much the same thing. Some people call it one thing, some others another thing.

Pressure Safety Valve (PSV)

Pretty much, if following ASME Sect VIII, it's a PSV.

Pressure Relief Valve (PRV)

Some people use PRV for liquid service and PSV for gas service. I don' know. Pretty much the same for me.

Pressure Safety Relief Valve (PSRV)

See above. Some valves are rated for both gas and liquid service. So I guess both the relief and safety in the name?

If I see any of the above acronyms, I am thinking a PSV.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[heaterguy]

So, to summarize:

PRV for liquid service
PSV for gas service
PSRV for liquid and gas service

 

[zdas04]

Works for me, like Ashereng if I see any of the terms I think "PSV". I always thought it was just regional dialects, but maybe not.

David

 

[pipehead]

All the terms are interchangable, vapor or liquid it doesn't matter, the valve doesn't care either.

 

[davsy]

There are a lot of examples of PRV being used for the Pressure Reducing Valve and PSV for the Pressure Safety Valve.

What do the relevant standards actully say about this. This is probably one of the more common uses of the same Acronym being used for different items depending upon what industry, company or even site you are on.

 

[heaterguy]

Per the Instrument Society of America:

Safety Valve (PSV): An automatic pressure relieving device actuated by the static pressure upstream of the valve and characterized by full opening pop action. It is used for gas or vapor service.

Relief Valve (PRV): An automatic pressure relieving device actuated by the static pressure upstream of the valve which opens further with the increase in pressure over the opening pressure. It is used primarily for liquid service.

Safety Relief Valve (PSRV): An automatic pressure relieving device suitable for use either as a safety valve or relief valve, depending on application.

 

[Ashereng]

heaterguy,

Yup.

Do be careful to clarify though. Not everyone follows these usage.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[davsy]

Heaterguy

Just as a matter of clarification according to ISA what should we be using for a Self Contained Spring or Pilot Actuated Pressure Reducing Valve such as you would find say on the main steam supply to a process unit.

As Ashereng said not everyone follows the usage and I have certainly seen it in various different ways.

 

[heaterguy]

Hi davsy,

ISA classifies pressure control valves in SP20 form 51. Relief valves are SP20 form 53.

HG

 

[stookeyfpe]

Don't forget burst disks and fusible plugs. Burst disks are recognized by the ASME BPV code and both pressure relief devices are recognized by CGA S-1.1 through S-1.3.

 

[JAlton]

NBIC (National Board Inspection Code)National Board of Boiler & Pressure Vessel Inspectors Repair & Inspection Code uses PRV (Pressure Relief Valve) for all types of Reclosing Pressure Relief Devices. Personally, I have always thought of PSV as Plant Safety Valve (an owner/user designation) which applies to any Safety (ASME Sec. I, Power Boiler) or Safety-Relief Valve (ASME Sec. VIII, Pressure Vessel). In some cases itmay refer to a non-code Liquid Relief Valve. I was not aware of ISA having designations. It took me years to say PRV instead of SRV, but I work with the NBIC VR (Valve Repair) Program, so I use PRV now.

JAC

 

[CJKruger]

heaterguy,

I am not totally sure, but believe the distinction between PRV and PSV is only important as regard to how far the pressure has to fall below set pressure for the valve to reset.

 

[JAlton]

I think what Heaterguy is referring to is the more strigent blowdown (i.e., reseat pressure) fro ASME Sec. I, Power Boiler Safety Valves versus the ASME Sec. VIII, Requirements for Pressure Vessels. However, as of ASME Sec. 2006 addendum, Power Boiler Safety Valves no longer have a maximum blowdown requirement. Ref PG 73.4.2.

JAC