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[US_ChemE]

Dear Forum Members,

 

We have received PSV sizing calculations from PSV supplier. Supplier has quated required relief area, selected relief area (actual orifice bore diameter) and rated capacity of the relief valve. This rated capacity is based on the coefficient of discharge and actual orifice bore diameter mentioned in the supplier calculation.  

 

For sizing PSV inlet and outlet lines, can we take the rated capacity furnished by supplier directly? Or do we need to divide it by 0.9 for calculating Theoretical maximum flow through selected PSV orifice considering that PSV supplier must have de-rated the co-efficient of discharge (ASME requirement - capacity certification) for its calculations?

 

Thanks & Regards,

US_ChemE

[fallah]

Hi,

 

Actually you don't need to divide rated capacity of the PSV by 0.9 and you can directly use the rated (or certified) capacity for PSV inlet/outlet lines sizing. You might worry about the actual PSV capacity (rated capacity/0.9) to be higher, then would create more pressure loss than that of using rated capacity. This concern appears to be reasonable, but in most cases the pipe size increament due to rounding up the calculated pipe size provide more room to compensate for any increment of actual flowrate respect to rated one...

 

Hope above elaborate the matter...

Edited by fallah, 04 April 2014 - 04:47 AM.