Pump manufacturers provide pump head curves showing the head, and efficiency as a function of the flow rate through the pump.  This knowledge base article describes the various landmarks found on a pump curve, and describes why it is so important to operate any centrifugal pump within the manufacturers prescribed limits.

Figure 1 shows a typical pump curve similar to those supplied by a pump manufacturer.  Various pump curve landmarks are displayed on the curve.  The PIPE-FLO and PUMP-FLO programs provide you with indication of these various points.

Figure 1 – Typical pump curve showing the major landmarks

Shut Off Head - is the condition of zero flow where there is no liquid flowing through the pump, but the pump is primed and running.

Minimum Flow – is the minimum capacity through the pump as specified by the manufacturer.  Operation of the pump below the minimum flow will cause damage to the pump.

Allowable Operating Range – (AOR) is that range of flows recommended by the pump manufacturer in which the service life of the pump is not seriously compromised.

Preferred Operating Range - (POR) is that range of flows specified by the customer around the pumps best efficiency capacity.  Continued operation within the preferred operating range extends the pump life further.  A recommend value for POR is between 70% and 120% of the BEP flow.

Rated Condition Point – is the capacity, head, net positive suction head, and speed of the pump, as specified by the customers order.

Best Efficiency Point – (BEP) is the capacity and head where the pump efficiency is a maximum.

Run Out – occurs at the end of the pump curve.  This is the maximum flow rate allowed by the manufacturer; operation of the pump beyond this capacity will cause damage to the pump.

References:
ANSI/HI 1.1-1.5 Centrifugal Pumps for Nomenclature, Definitions, Application and Operation
ANSI/HI 9.6.3 Centrifugal / Vertical Pumps Allowable Operating Range