Pilot PSV overpressure

[causeandeffect]

hi folks,
I am looking for a pilot operated relief valve (set pressure @ 214 barg to flare b.p 10 barg max)that will pass full flow of gas (PSV full opened)with absolutely no overpressure, i.e. at full relief the pressure upstream PSV is 214 barg only. I understand that is one attribute of pilot operated psv.
thanks

 

[dcasto]

A regular or spring loaded PSV will start opening at the set pressure, but will be fully open by 10% of the set pressure. A pilot operated goes full open at the set pressure. There are some tolerances allowed be the code so it will be 214 barg +/- a percentage allowance (very small but the design codes allow for this too).

As for brand, ther are lots, Mercer, Taylor, Consolidated, Axelson,

 

[Ashereng]

You can also add Farris and Anderson Greenwood Crosby as vendors with good products.

"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?

 

[djack77494]

C&E,
If you specify a valve that will pass your full flow at 204 bard (bars differential), then you should not have any overpressure other than the normal hardware tolerances. Yours would not be a "normal" specification, so work with the vendor to ensure he/she understands your requirements. I don't see why you are inclined towards a pilot operated PSV, though one would certainly be acceptable. (But so would other types of PSV.)
Doug

 

[causeandeffect]

many thanks All, I chose pilot psv for capacity reason and so reduce number of psvs required

 

[dcasto]

Another thing you can specify on pilot PSV's is that they Thottle or modulate the relief, that way the PSV will not cycle or chatter.

 

[JLSeagull]

Consider pilot operated PSV's for clean fluids.

 

[robsalv]

Causeandeffect, seems odd that you want to avoid any accumulation. The SV is presumably protecting a pressure vessel which should have been hydrotested to 1.3 to 1.5xDP depending on code and construction year.

A pilot is a good choice if you want seat tightness up to ~97% of set pressure. A modulating pilot is better than a pop acting in that it will elliminate full capacity releases for small contingencies or upsets - and also as stated, reduce chatter. You might need to have the set pressure lowered though in order for the maximum opening to occur at your desired pressure.

Are you sure you have the contingency nailed? What if someother contingency can generate more capacity than the SV can handle?? Pressure will definitely go above set pressure then.

You could equally use a conventional SV with a reduced set pressure, designed for full flow at the 10% accumulation equalling your desired pressure. That's been done in my work place before, but normal operating pressure needs to be well controlled or else spurious lifts can occur.

Definitely definitely concur with the clean service requirements for POSV's.