SIZING DATA

PUMP CAPACITY: Multiply the developed boiler H.P. by .07 to determine the evaporation rate of the boiler (expressed in gallons per minute). Next, multiply this evaporation rate by 3 to determine the capacity of the feed pump (in G.P.M). This factor of 3 allows the pump to cycle at reasonable intervals. If one boiler is being fed, a simplex unit may be used, but a duplex unit (with each pump sized to independently feed the boiler) has the advantage of providing an emergency standby pump or alternating the pumps for even wear. If two boilers are being fed, use duplex unit and size one pump for each boiler (specify 4-pole double throw transfer switch to cross pump-boiler assignment) or use triplex unit with each pump sized to feed one of the boilers (specify transfer switch to use one pump for standby service).
PUMP DISCHARGE PRESSURE: Discharge pressures in the Engineering Selection Table are pressures at the pump. To compute, add boiler working pressure plus static head (from pump center line to boiler connection center line) plus discharge line friction loss (including pipe, fittings, valves, etc.). Convert all factors to P.S.I. before adding. Static head plus friction loss plus a small residual pressure can be estimated at 5 P.S.I. in most cases.
RECEIVER SIZE: Allow approximately one gallon of receiver capacity for each H.P. of boiler(s) being served. (Example: If two (2) 250 H.P. boilers are being fed by a duplex unit, receiver should have 500 gallon capacity.