Gene Vogel
EASA Pump & Vibration Specialist

Vertical turbine pumps (VTP) are driven by vertical motors with large thrust bearings that support the weight of the motor rotor, the pump rotor and the dynamic down-thrust generated by the pump impellers as they lift the liquid. The weight of the motor rotor and pump rotor are easily determined from simple engineering data. The amount of thrust generated by the impellers as they interact with the moving liquid is much more complicated, and the thrust is not always generated in the downward direction.

During certain stages of pump operation, the flow of the liquid through the impellers can generate an upward thrust that can lift the pump rotating assembly. The resulting upward force can cause havoc with thrust bearings in the motor which may be designed to handle only down-thrust. 

This article will briefly review how pump up-thrust occurs and the provisions of VTP motors designed to control it.

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