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Posted by Bob D. on December 29, 2003 at 07:11:45:
In Reply to: PLease Help with Safety Valve Capcity Calculation posted by Al the boiler guy on December 25, 2003 at 18:26:37:
Al, I'm not sure where you got your equation from, or where some of the values you show came from. For example, be real careful that the actual discharge area (seat or poppet) is used, and not simply the valve inlet connection size. There are also a few other factors that even simple "cookbook" equations need to allow for, such as discharge coefficent. Anyway,
If you use the ASME Section 1 "cookbook" approach:
P = 47.7 PSIA
A = 3.14 sq. in. (assume your 2" dia is O.K.)
Kd = 0.9, discharge coefficient
Ksh = 1 (saturated)
Kb = .9 (atmospheric backpressure)
Kn = 1.0 (Napier steam correction factor)
so,
W = A*51.45*Kd*P*Ksh*Kb*Kn = 6,242 lbm/hr
which is within 5% of the 6,530 you state. Based on the string of assumptions, and no allowance for vessel overpressure from setpoint (accumulation), I figure that's in the ballpark.