A pump curve can be a valuable tool, not just for pump selection, but for troubleshooting and system optimization. Detailed information on a pump curve provides insight which can save time and energy which equates to operating dollars. The value that can be gleaned from the curve is directly proportional to the information that is available to the pump, operation, fluid and attached systems. This holds true whether the pump is in an operating real world system or part of a model in hydraulic analysis software like PIPE-FLO® Professional.
The pump curve on its own is just a representation of the potential and range of the pump. This can provide enough information to know if the selected pump will generally work for the desired application, but not necessarily how well it will perform. For actual performance characteristics of the pump in operation, more details about the pump, fluid, and system are needed.
The first order of business is determining the specific curve by using the design and system data of the pump’s hardware and operating conditions; impeller size, pump speed, and fluid properties. Knowledge of the Impeller size (8.125in) and speed (3550 rpm) will narrow the range of possibilities to just a single curve. Actual test data for impeller and speed changes is preferred, though predictions of performance can be made with proper use of the Pump Affinity Rules. Where the fluid pumped is significantly different than the test fluid, the curve can also be Viscosity Corrected for an accurate prediction of performance with the current fluid.
With the corrected curve now representing actual pumping configuration, the flow rate or head of the pump can be used to determine the specific operating point on that curve. Specific values for efficiency, power, and NPSHr can be calculated or read from the graph. This is where the true value of the curve as a prediction tool becomes apparent. How close is it running to the best efficiency point, (BEP) and will this impact maintenance? How much can flow be changed while remaining in the preferred operating region? Is this pump a good fit for the full range of flows anticipated for normal operation? Is the Net Positive Suction Head required, more than what is available to the pump suction? A paper or digital curve with sufficient operation information will answer these questions.
Understanding the total picture allows users to make intelligent corrections. The true value of a clear picture of the pump curve and the ability to use it as a prediction tool becomes apparent, particularly when combined with a simulation program. With PIPE-FLO® users have this ability and more.