How to Read a Centrifugal Pump Curve

At first glance, with no prior knowledge, a pump curve can be quite intimidating to decipher. There are an array of different curved lines, straight lines, values, and tables. Knowing what information to look for can simplify this task significantly.

Below is a simple centrifugal pump curve though not all data sheets will have this arrangment. In this case, I have searched for an ANSI pump to produce 300 US gpm of flow of ambient temperature water at 100 ft of head, resulting with a 2×3-13 pump such as a Pinnacle-Flo 8896 MT1, Goulds 3196 MT, or Peerless 811M. The first thing I look at is the curve itself. The large, yellow region is the recommended operating zone bounded on the left by the red, minimum flow line and vertically by the max and min impeller trim sizes. The red marker denotes our search point (Flow: x-axis, Head: y-axis) whereas the point on the adjacent black curve (impeller trim: 10.75”) shows our Best Efficiency Point (BEP) at 64.3%. This means the pump can perform at 64.3% efficiency where hydraulic, volumetric, and mechanical losses are at their lowest. Our design point is not far from the BEP, as both are about 64%, which is in the expected 50-70% range for smaller centrifugal pumps. From this information alone, we have a good pump pick. Deviating too far left or right from this point will decrease pump, bearing, and mechanical seal life and can lead low/high flow cavitation.

The table surrounded by the black box contains what may be the most important information when installing the pump into a piping system. The values here show motor load, minimum net positive suction head (NPSHr), shutoff head (no flow), and minimum flow. The remaining information is rather straightforward. The Pump heading contains information about the pump (size, type, RPM, and impeller trim). The Fluid heading has info about our fluid to be pumped. The fluid properties are dependent on the fluid itself with respect to process temperature. The motor heading displays the suggested motor power, type, speed, and frame size. The Pump Limits heading is used less often but it useful in unusual/extreme conditions or when solids are present in the process fluid.

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