Best Efficiency Point (BEP)
The best efficiency point (BEP) is the flow and head at which a pump operates at its maximum efficiency for a given impeller diameter and speed. At BEP, liquid enters and leaves the impeller vanes at angles close to their design values, so hydraulic losses, radial thrust and internal recirculation are at a minimum. Operating well to the left of BEP can cause suction or discharge recirculation, heating and vibration; operating far to the right can increase NPSH required and lead to cavitation. API 610 defines a preferred operating region of 70% to 120% of BEP flow and requires the rated point to lie within 80% to 110% of BEP flow. Keeping duty points close to BEP extends bearing and seal life and reduces energy consumption. With a VFD, the BEP shifts with speed per the affinity laws.
Examples
- Checking a rated duty point against the API 610 preferred operating region
- Trimming an impeller to bring the duty point closer to BEP
- Using a VFD to keep a variable-flow pump near BEP