How do centrifugal pumps work?

Centrifugal pumps are one of the most common machines in the industrial landscape. The technology relies on two central components: an impeller, and a volute casing which contains the impeller and the cased fluid.

The pumps are available in a wide variety of sizes. Axial centrifugal pumps in municipal water applications can be very large, whereas they can be small and compact in domestic systems.

The basics of how they work

Fluid enters the pump through an inlet positioned at the centre of the impeller, or the 'suction eye'. Friction between the liquid and the surface of the rotating impeller causes the fluid to rotate. The rotating fluid is then thrown to the outside of the impeller by centrifugal force. It is this phenomenon that causes objects revolving around a centre point to move away from the centre. This is how the fluid gains kinetic energy.

The amount of energy added to the fluid is dependent on three factors; the density of the liquid, the impellers speed of rotation; and the diameter of the impeller.

From the impeller, the liquid is released into the chamber of the volute casing and directed to the discharge outlet, and ultimately into the system.

The pump design allows for high flow rates with low pressure. The design also creates a pulseless flow which makes them well suited to continuous pumping duties.

A common misconception is that the curvature of an impellers vanes help to move fluid by trapping and pushing it through the pump. In reality, the vanes purpose is to conduct the liquid across the smoothest possible path as it travels through the pump. Backwards curved vanes, for example, help to stabilise flow conditions at high speeds and reduce demands on the motor of the pump. It is, therefore, possible to tell the correct rotation of an impeller by looking at the curvature of the vanes.