What Is BEP for Boiler Feed Pump?
BEP means best efficiency point. It is the flow and head where pump efficiency is highest and vibration is lowest. For feed pump, BEP is usually marked on pump curve sheet as peak of efficiency curve.
Running at BEP gives lowest power per m³, longest seal and bearing life, and lowest noise. Running far from BEP causes recirculation inside impeller, high temperature rise and cavitation.
BEP Formula and Operating Check
Percent BEP = (Q_operating / Q_BEP) × 100Power: P = rho × g × Q × H / (eta × 1000) [kW]Efficiency off BEP: eta_op ≈ eta_BEP × [1 - 0.35 × (r -1)²] where r = Q_op / Q_BEP
POR = 70% to 120% BEP - preferred, AOR = 60% to 130% BEP - allowable
Ns = N × sqrt(Q) / H_stage^0.75 , H_stage = H_total / stages
If you run at 60% of BEP, efficiency may drop 5-10 points and power per m³ goes up. That extra power becomes heat and vibration.
How to Use the Calculator
- Get BEP from curve. Look at pump datasheet, peak efficiency point flow, head and efficiency.
- Enter operating flow. From flow meter or from boiler steam flow plus blowdown and recirculation flow needed at low load.
- Enter operating head. If throttling valve is used, head rises a bit. If VFD is used, head falls.
- Click Check BEP. See percent BEP, POR/AOR status and extra power lost.
Understanding Results
Percent of BEP
100% is ideal. 70-120% is preferred operating range where life is normal. 60-70% and 120-130% is allowable but with more vibration. Below 60% or above 130% is outside range and risky for long term.
Efficiency Drop
Efficiency falls off on both sides of BEP. At 60% BEP, expect 5-8% lower efficiency. At 130% BEP, also lower. Calculator uses simple parabola, so check real curve for exact.
Extra Power Lost
Difference between power at actual efficiency and power if you were at BEP efficiency for same flow and head. Multiply by hours per year to get wasted energy.
Why BEP Matters for Feed System
Feed pump is high pressure, multistage. Running far from BEP causes high radial load, seal leak and impeller wear. It also heats water and can flash in deaerator return line.
Before you check BEP, you need correct head. Use our feed pump sizing system to get flow, TDH and power at full load. That gives you base for BEP check and helps set affinity law correction for VFD speed.
- Too low flow: Pump runs hot, needs recirculation valve open, cavitates at suction.
- Too high flow: Pump may run past end of curve, overload motor and lose NPSH.
- Best practice: Keep boiler feed pump between 70% and 120% BEP most of the time. Use VFD or two pumps in parallel to cover low and high load.
Worked Example
Pump BEP 60 m³/h, 130m, 68% efficiency. Operating 38 m³/h, 138m, 2950 RPM, 5 stages, 8000 h/yr.
| Step | Calc | Result |
|---|---|---|
| Percent BEP | 38/60×100 | 63.3% |
| POR low/high | 0.7×60 to 1.2×60 | 42 to 72 m³/h |
| Status | 63.3% between 60-70 | Allowable, not preferred |
| Efficiency est. | 68×[1-0.35×(0.633-1)²] | 64.8% |
| Power at BEP (for 38 m³/h) | 9.81×0.0105×138 /0.68 | 20.9 kW |
| Power actual | 9.81×0.0105×138 /0.648 | 21.9 kW |
| Extra loss | 21.9-20.9 | 1.0 kW, 8000 kWh/yr |
Frequently Asked Questions
What is BEP of a pump?
Best efficiency point where pump efficiency is maximum. It is the ideal flow and head for that pump and speed.
What is POR and AOR?
POR is preferred operating range 70-120% BEP for long life. AOR is allowable operating range 60-130% BEP for short periods.
Can I run pump at 50% BEP?
Only for short time with recirculation open. Long term at 50% causes heat, vibration and seal wear.
How to find BEP?
Look at pump curve. BEP is where efficiency curve peaks. If curve not given, BEP is near 80-90% of max flow at rated speed.
Basis: Hydraulic Institute ANSI/HI 9.6.3 and 9.6.7 for POR/AOR, Grundfos and KSB multistage feed pump curves. Efficiency off BEP estimated by parabolic drop, actual may vary. Specific speed per Hydraulic Institute definition with head per stage. Check maker curve for exact efficiency and min flow.