water pump working too hard?

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Reef Keeper
Jul 5, 2003
You will only know by measuring the pump motor amp draw at the motor. If it is drawing more amps than the Full Load Amps (FLA) rating on the motor label, there is a serious risk of burning out the motor. To reduce the amp draw, do one of three things: (1) Get full voltage to the motor by using heavier wiring; (2) Restrict the pump discharge; or (3) Trim the impeller.

(1) Check the voltage at both the pump and the source. If it is less than 5V (or more) at the pump, a heavier gauge wire will reduce the voltage drop and, thus, the amp draw.

(2) Pump discharge can be restricted by using a valve, but there is a risk of someone opening the valve later. In place of a valve, use a permanent restriction, such as a reducer fitting in the discharge pipe.

(3) To trim the impeller, remove the pump case (volute) and very carefully trim 1/8” off the impeller diameter. In some cases, this can be done by very carefully holding a file to the impeller while the pump is on. Put the pump back together and test the amp draw again. Repeat the trimming procedure until the desired amp draw is achieved. Remember that trimming reduces the gpm.

To be absolutely certain that motors won’t fail due to excessive amp draw, do the following: In many places with 110-120V service, a voltage variation from 105 to 126 may occur. A motor’s amp draw will be the highest when the voltage is the lowest, so check the full load amps when the facility’s voltage is lowest and while all other equipment on that circuit is in use. Always check volts and amps at the motor while the pump is running at full load.