Boiler Feed Pump Calculation
Size a boiler feed pump: required flow, total dynamic head, hydraulic and brake power.
Inputs
Overcapacity above steam demand (industry norm 10–15%).
Boiler operating pressure + safety valve + line loss.
Affects specific gravity and NPSH available.
Results
Formula
Q (GPM) = Steam flow × margin / (500 × SG); TDH (ft) = 2.31 × (P_d − P_s)/SG + static + friction; Brake HP = Q × TDH × SG / (3960 × η_pump).
Worked example
A boiler evaporating 10,000 lb/hr at 200 psig, with 10% margin, 220°F feedwater, 65% pump / 92% motor efficiency: Q ≈ 22 GPM, TDH ≈ 476 ft, brake HP ≈ 4.1 HP, motor input ≈ 3.3 kW.
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Frequently asked questions
Why add a 10% design margin?
Boilers experience swings in demand, and pumps must handle both blowdown make-up and peak firing rates. 10–15% margin is standard practice.
Which pressure should I enter as discharge?
Boiler operating pressure + safety-valve setting margin + line friction losses to the boiler inlet. Do NOT use just the boiler drum pressure.
How does feedwater temperature affect sizing?
Hot feedwater lowers specific gravity, which slightly increases flow (GPM) requirements and reduces NPSH available — a common cause of BFP cavitation.
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