Relief Valve

Hai,

In general if the set point is 100 psi, it may give leakage from 60 psi and it will give huge leak at 100 psi, this what we observed with new relief valve.

G.Rajesh

Is there any specific procedure for this relief valve testing?

Set pressure will vary according to the purpose. Generally relief vale set at 10% above the working pressure.

Relief valve should check at their places on line.But for the approximate setting, you can test the relief valve by hydro pump.

You should test it according to the manufacturer's instructions. Relying on anonymous "experts" (who may actually know nothing) might get someone killed.

No offense to previous posters, but we don't know application or manufacturer.

I am not sure as to how fully there is a standard for this. But from what I understand, a relief valve should start to open at its set pressure, and should attain its rated flow capacity at 10% "accumulation pressure" above this. Because of manufacturing tolerances, a relief valve might "weep" or "simmer" (i.e., start to open) at some lower pressure such as 90% of its rating.

For this reason, it is typical to design a system so that pressure switches will shut off compressors about 15-20% below the relief valve ratings.

I am not familiar with testing relief valves in the field, which seem inadvisable anyway. Instead, relief valves are typically replaced periodically, or sent out to certified shops for recalibration.

Hi Tornado,

In situ Trevi testing of relief valves is now accepted by many (most?) authorities.

Beats hell out of the old system of scaring oneself half to death when valves popped while sitting on top of a boiler floating the steam SRV's.

Interesting thought, but I don't know if I can use it. Ammonia refrigeration falls under ASHRAE-15 (1994 and amendments) and IIAR (International Institute of Ammonia Refrigeration). Relief valves are to be renewed (or recalibrated by ASME certified shop) every 5 years. The most common set-up consists of a diverting valve with two relief valves. Isolating one for service ensures that the other is on line.

While changing out a valve, one must hope that no other relief valve discharges into a common header....

I do not know about ASHRAE, but Trevitesting is accpeted by ASME to the best of knowledge. Extract from a Furmanite article: Trevitest is widely accepted by safety authorities and industrial insurance companies in all the key areas of operation including ASME and National Board in the USA, the HSE and Lloyds Industrial Services in the UK and the TUV in Germany. In addition approvals for the Trevitest have been given by many well known companies in the oil, petrochemical, fertilizer, power generation and other process industries.

It has saved me a lpt of time, money and heartache. Having said that, I still do them in the shop if I get the opportunity for a shutdwon or the like.

First a bit of a rant - we do not need a GA or off topic rating, we need a "bad engineering" or "dangerous advice" rating button.

Guest,

If a Safety Relief Valve is set to open at 10 bar then it MUST open at 10 bar. It does not gradually open. If it does then it is not a relief valve. (Dump valves or cheap and nasty pressure regulating valves behave that way, not relief valves).

To give a rough example, a 10 bar relief valve should be subject to a Seat tightness Test. With the air or nitrogen pressure held steady at 90% of set pressure (9 bar), a 7.9 mm tube immersed 12.7 mm deep in water (taking the leakage past the seat of the relief valve) should allow no more than 40 bubbles a minute leakage for metal to metal seats, and ZERO leakage for soft seats. (So don't listen to anything that poster # 1 says on this subject, it could get somone killed.)

By the way, 40 bubbles per minute works out to around 0.017 standard cubic meters of air or nitrogen every 24 hours, so these things are meant to be pretty tight.

I can think of the following standards, I am sure there are more:

API 502 Part 1 & 2 - Sizing selection, installation etc of RV's

API 527 Seat Tightness testing

API 526 Flanged RV's

ASME Boiler and pressure vessel code - set pressures

ASME PTC25 - something to do with pressure relief devices.