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The two terms seem interchangeable and I can't find a strict definition for both, so what's the difference between them if there is any?

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An impeller is the type of rotor found in a centrifugal pump, in fact another name for "centrifugal pumps" is "impeller pumps". Many different types of pump have rotors.

The pump "rotor" is simply a term the rotating components of the pump. Gear pumps, sliding vane pumps, swash-plate pumps, and circumferential piston pumps all have rotors, but none of them have impellers

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  • $\begingroup$ But I have an inspection test plan for a centrifugal pump that requires a dynamic balance for both the rotor and the impeller how can that be? $\endgroup$
    – Algo
    Apr 13 '16 at 4:21
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    $\begingroup$ Perhaps the plan means the rotor as the rotating components that are part of the pump such as the seal, shaft etc. and the impeller as solely the rotating component that acts on the water. I'd ask for clarification from the people who gave you the test plan, it sounds unclear. $\endgroup$
    – DLS3141
    Apr 13 '16 at 5:00
  • $\begingroup$ I found that API 610 defines rotor as "assembly of all the rotating parts of a centrifugal pump". $\endgroup$
    – Algo
    Apr 13 '16 at 17:47
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A centrifugal pump consists of two main components

  1. Electric motor
    It is usually an induction motor. All electrical engineering courses would cover this in the lower year.
    An electric motor has two components

    • Stator - It is the stationary part of the motor. Electricity is supplied to terminals on the stator.
    • Rotor - It is the rotational part of the motor. It is supported on bearings and mechanically coupled to external device, such as impeller in this case.
  2. Impeller
    This is the rotational part of a centrifugal pump or a compressor. It is used to increase the pressure and flow of a fluid. As it is coupled to the rotor of a motor and rotational, it is also called rotor.

Induction motor has very limited speed control, hence variable speed drive (VSD) is used to supply variable frequency and voltage to the motor, enabling the later to run at different speed, and hence driving the impeller to operate at different pressure and flow rate.

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