hi all,
i need to perform sizing calculation of Pressure Relief Valve (PRV) for Fire Water System. According to NFPA 20, if 121% of shuttoff pressure + max static pressure exceeds the rated system components, PRV shall be installed. in my case, the pressure is above the max allowable pressure for the fittings (around 250 psig), so i shall design the PRV.
i once design the PSV for gas application (Blocked discharge / fire governing case ). but i have confussion to size the PRV for my fire water system (1000 gpm). should i design PRV based on API 520 ? or NFPA 20 ? because in table 2-20 NFPA 20 (1999 edition). it is stated that the minimum relief valve size for 1000 gpm is 4 inch. i dont understand, because usually i calculate the area of orifice which is in square inch, not in inch. could you please guide me ?
if i decide to calculate based in API 520 , i need to determine the back pressure (which is pressure drop from my fire water pump to fire hydrant , isn't it ? ) i need a balanced below PRV because if my back pressure is 85 psig, it is less than 30% of my set presure (250 psig). am i right ?
please enlighten me
i need to perform sizing calculation of Pressure Relief Valve (PRV) for Fire Water System. According to NFPA 20, if 121% of shuttoff pressure + max static pressure exceeds the rated system components, PRV shall be installed. in my case, the pressure is above the max allowable pressure for the fittings (around 250 psig), so i shall design the PRV.
i once design the PSV for gas application (Blocked discharge / fire governing case ). but i have confussion to size the PRV for my fire water system (1000 gpm). should i design PRV based on API 520 ? or NFPA 20 ? because in table 2-20 NFPA 20 (1999 edition). it is stated that the minimum relief valve size for 1000 gpm is 4 inch. i dont understand, because usually i calculate the area of orifice which is in square inch, not in inch. could you please guide me ?
if i decide to calculate based in API 520 , i need to determine the back pressure (which is pressure drop from my fire water pump to fire hydrant , isn't it ? ) i need a balanced below PRV because if my back pressure is 85 psig, it is less than 30% of my set presure (250 psig). am i right ?
please enlighten me