SPRING SET PRESSURE

[10108322]

FOR A CONVENTIONAL SAFETY VALVE... WHICH SHOULD BE THE SPRING SET PRESSURE... I'VE READ TWO ARTICLES... AND THEY SAY:

1) SPRING SET PRESSURE= SET PRESSURE-SUPERIMPOSED BACK PRESSURE - BUILT UP BACK PRESSURE

2) SPRING SET PRESSURE=SET PRESSURE - SUPERIMPOSED BACK PRESSURE

WHICH ONE OF THESE DEFINITIONS IT'S OK?

 

[786392]

Dear 10108322 Hello/Good Morning,

Is there real need to use Block Capitals;I consider this inadequate here.



Best Regards
Qalander(Chem)

 

[lizking]

For conventional RVs, a constant (stress CONSTANT) superimposed backpressure is subtracted from the set pressure to obtain "spring setting" or CDTP (cold differential test pressure). Built-up backpressure is NOT included.

Note: caps used for emphasis.

 

[sheiko]

On most conventional valves where superimposed back pressure exists, the back pressure is compensated for during production testing. In most cases the compensation is on a straight differential basis. As such, a valve that has a set pressure requirement of 100 psig but will be installed in a system where there is 10 psig constant superimposed back pressure will be net set on the test stand at 90 psig (relative to you, it opens at 100 psig, relative to the spring, it opens at 90 psig. The pressure in the vessel will be 100 psig on a pressure instrument). This is sometimes called the differential test pressure. A further variation of this is the cold differential test pressure (CDTP) which also takes the effects of temperature into account.

So, differential test (or set) pressure should only address the constant portion of the superimposed back pressure (There is sometimes a “variable superimposed” portion. This type of back pressure varies or changes over a range from a minimum to a maximum, or vice versa. The actual back pressure at any specific time depends on conditions in the piping system to which the outlet of the valve is connected).

P.S: Could you please give us the references of the 2 articles you have mentionned?

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