Boiler Feed Pump Sizing: A Practical Guide
Boiler Feed Pump Sizing
Sizing a boiler feed pump (BFP) starts with three numbers: the boiler's steam production, the operating pressure, and the feedwater temperature. Get any of them wrong and the pump will either cavitate, hunt, or waste energy for its whole life.
1. Design flow
Start with steam demand in lb/hr, add 10–15% margin for demand swings and blowdown make-up, and convert to GPM using the correct specific gravity for hot water.
2. Total dynamic head (TDH)
TDH = pressure head + static suction lift + friction losses. Use the boiler operating pressure PLUS safety-valve setting margin, not just drum pressure.
3. NPSH available
Hot feedwater is the enemy of BFPs. As temperature rises, vapor pressure rises and specific gravity drops — both cut NPSH available. Deaerator elevation and suction pipe design matter more than most engineers realize.
4. Common mistakes
- Sizing on nameplate steam flow only
- Ignoring safety-valve setting in TDH
- Underestimating friction in suction piping
- Using the wrong SG for hot water
Use our Boiler Feed Pump Calculator to check your work.
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