Pump Impeller Tip Speed

Wear in Centrifugal Pumps

Excerpt from the Dec. 2019 Pumps & Systems Article by Gary Dyson

Tips to recognize and reduce erosion and abrasive wear

Centrifugal pumps are sometimes used in environments where the pumped product contains suspended solids. While some pumps are specifically designed for solid handling or slurry applications, normal centrifugal pumps do not contain features to prevent performance degradation from the impact of solids.

There are a few key signs that a conventional centrifugal pump is suffering from erosive and abrasive wear. Here are assessment and mitigation strategies to be considered and applied when this occurs.

Particles are a problem in a centrifugal pump due to the way the machine adds velocity to the liquid as it passes up the impeller channels. In general, the higher the speed at the tip of the impeller, the more energy that is imparted to any particle that is suspended within the liquid. This energy can then cause damage to anything it impacts.

Pump Impeller Tip Speed

It is important to draw the distinction between tip speed and rotational speed. A small diameter impeller running at high speed could have a lower tip speed than a large diameter impeller running slowly. Tip speed is the velocity of the impeller at its outside diameter.

In general terms, the material loss by erosion is determined by the velocity of the particle cubed (Equation 1).

Equation 1:
Erosion = XC3

C is the velocity of the particle
X is a coefficient based on the liquid
being pumped

The velocity of the particle is directly associated to the tip speed of the impeller (Image 1). Lowering the tip speed of a machine has a significant impact on particle velocity and, thus, the erosive energy.

Volute Tip Wear

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