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5 causes of pump shaft displacement

The purpose of the shaft within a pump is to transmit an electric motor’s rotational power to its impeller. The shaft, therefore is an essential component, and if it should become displaced there may be a significant reduction in the pump’s energy efficiency and reliability.

Here are five common reasons for pump shaft displacement.


Cavitation is a common problem and occurs when bubbles form in a liquid before collapsing and causing shock waves within the pump. These shock waves can be severe enough to displace or even break the shaft. Cavitation may be avoided by reducing the motor’s rpm where possible, increasing the diameter of the impeller eye or using a double suction impeller.


Pump vibration can have several causes, with one of the most common being worn bearings which disrupt the shaft’s natural position. Vibration should be avoided by ensuring bearings are properly lubricated and replaced as necessary.

Water hammer

This refers to a surge of pressure created when liquid stops or changes direction suddenly, usually when a valve is closed abruptly within a pipeline. The pressure wave created can be very destructive and is powerful enough to dislodge the shaft.

Pipe strain

Pipe strain relates to unwanted pressure or movement within piping systems, with one of the consequences being shaft misalignment. Causes of pipe strain include poor design or installation, thermal or mechanical expansion and process changes.

Deviation from best efficiency point (BEP)

BEP represents the point on a pump curve that produces the optimum level of efficiency. When BEP is achieved, bending forces are distributed evenly around the pump’s impeller and components are protected. However, should the pump operate off BEP, an imbalance will occur which may cause shaft deflection.

As long-time suppliers, installers and repairers of pumps for all commercial, industrial and agricultural processes, there isn’t much we haven’t seen. So if your pump-powered application is running poorly, give Matthew Gibbons a call on 07970 676272 or email for expert assistance.

Pumps & Controls

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