Coefficient of Discharge for Safety Relief Valve Sizing
Coefficient of Discharge for Safety Relief Valve Sizing
(OP)
Hello.
I have a question concerning Safety Relief Valve coefficients of discharge (Kd). Consider a case where an ASME stamped safety relief valve (for a Sec. VIII, Div. I application) is installed with liquid trim. Assume the conventional safety relief valve has a Kd value of 0.7 for this liquid trim. Also assume the same safety relief valve has a gas/vapor Kd value of 0.9 when installed with gas/vapor trim. My question is if one is to now consider a sizing case for all vapor relief, what Kd value would you use for this safety relief valve since it is installed with liquid trim? 0.9 or 0.7? A similar case would be just the opposite, where an existing SRV is installed with gas/vapor trim and is subject to all liquid relief. Is the Kd value a function of the installed trim? Thanks in advance for any help.
I have a question concerning Safety Relief Valve coefficients of discharge (Kd). Consider a case where an ASME stamped safety relief valve (for a Sec. VIII, Div. I application) is installed with liquid trim. Assume the conventional safety relief valve has a Kd value of 0.7 for this liquid trim. Also assume the same safety relief valve has a gas/vapor Kd value of 0.9 when installed with gas/vapor trim. My question is if one is to now consider a sizing case for all vapor relief, what Kd value would you use for this safety relief valve since it is installed with liquid trim? 0.9 or 0.7? A similar case would be just the opposite, where an existing SRV is installed with gas/vapor trim and is subject to all liquid relief. Is the Kd value a function of the installed trim? Thanks in advance for any help.





RE: Coefficient of Discharge for Safety Relief Valve Sizing
For preliminary sizing you can use Kd=0,65
RE: Coefficient of Discharge for Safety Relief Valve Sizing
Compare this to the documentation of the current worst case scenario. There should be a minimum required area, Aliquid, calculated for that.
If Avapor > Aliquid, the worst case scenario changed and you must change the trim. If Aliquid > Avapor, the liquid case is still the worst case scenario and don't change the trim.
If you had a 2-phase flow scenario, you'd use Kd = 0.9 for that and calculate A2-phase. The largest required area of the three flow phases will determine the size and trim of the relief device.
Good luck,
Latexman