Rated Condition Definition

What is a Pump’s Rated Condition?

The rated condition is the operating point a pump is designed to operate at, and the primary condition at which operation is verified during a pump performance test.

If a pump system is designed around a pump which produces a flow of 1000 GPM at 100 Ft, and the pump must demonstrate performance at that condition during a pump performance test, then 1000 GPM at 100 Ft is the rated condition for that pump.

A rated condition may also be called a guarantee point or the primary operating condition.

The rated condition usually represents a point at which the pump will operate continuously. As a result, it is usually advisable to locate the rated condition within a pump’s preferred operating range (POR), and the rated condition should always be located within a pump’s allowable operating range (AOR). In most cases, the rated condition should be located as close to the best efficiency point (BEP) as possible.

During a pump performance test, the pump curve must be found to pass very near to the rated condition. Test tolerances vary depending on the test standard applied. However, one common standard states that the pump curve must pass within 5% of the rated head at the rated flow and +/-10% of the rated flow at the rated head. For example:

  • Rated condition: 1000 GPM at 100 Ft
  • Test tolerance: +/-5% of rated head at the rated flow and +/-10% of the rated flow at the rated head.
  • Head tolerance: Head must fall between 95 Ft and 105 Ft when measured with the pump operating at 1000 GPM.
  • Flow tolerance: Flow must fall between 900 GPM and 1100 GPM when measured with the pump operating at 100 FT TDH.