Special Pressure Relief Valve Manufacturer

[zaideeo]

Hi All,
Problem :
Looking for pneumatic pressure relief valve (PRV) that will only relief to a required pressure. Example :

Operating Pressure : 70 psig
Relief Pressure : 72 psig
Default Relief Pressure : 35 psig - preset at factory/non adjustable
Required Relief Pressure : 68 psig

We have an airbag system that controls the tightness of the press roll on our papermachines. The PRV that protects the airbag is set to pop at 72 psig. Normal operating pressure is around 70 psig. When the PRV pops, it reliefs all the way down to 35 psig, which makes the press rolls really loose and we start loosing paper. We require it to relief on to a preset pressure around 68 - 65 psig and not much less to avoid loosing paper.

Question :
Anybody know who manufacture such PRV?

Appreciate your inputs. Thank you.

 

[owlscreech]

The drop in pressure drop before reclosing is called blowdown. For a ASME Section VIII (UV Stamp) valve it should be about 7% of the set pressure or 3 psid whichever is greater. For you then it should be 5 psid. Your blowdown is about 50%. For a safety valve, blowdown is usually adjustable through an opening opposite the outlet. Sometimes there are two openings to make other adjustments to achieve better lift characteristics.

While you should be able to adjust it, my recommendation is forget it. Buy a UV stamped valve. You should be able to shop the web for a new one and get names (Consolidated, Kunkle, Anderson-Greenwood, etc.) of folks who make them. If your valve is not ASME (the application you describe doesn't appear to need one if the valve is only protecting the airbag), then it may not have bought that way.

Why are you operating so close to setpoint? Do you have many lifts?

 

[spud1]

You may want to consider a modulating pilot operated valve which would give the least working/set pressure differential combined with the lowest blowdown. Further details and links are in thread408-52271 - "pilot operated safety valve" in this forum.

 

[JAlton]

Not all Pressure Relief Valves have adjustable blowdown.
You use the term preset to refer to the reseat pressure.
Blowdown is the difference between popping pressure and reseating pressure. I would suggest an Anderson Greenwood type 81 with Adjustable Back Pressure Compensated Closing and O-Ring Seats. This is not nearly as expensive as a Pilot Operated Valve and should be able to achieve 5 to 7% blowdown with no problem. If you have it set for 70 psig it should close around 65 to 67 psig. The o-ring seat has superior seat tightness compared to metal seated PRVs and the back pressure compensation means the blowdown can be adjusted precisely without affecting the set pressure.

J. Alton Cox
President
DeLuca Test Equipment

http://www.delucatest,com

 

[MortenA]

spud1 has the answer: Modulating pilot operated PSV.

Anderson greenwood e.g. makes them:

http://www.andersongreenwood.com/posrvprod.asp

Best regards

Morten