An internal gear pump is a type of positive displacement pump, characterised by an external gear (driving gear) and an internal gear (driven gear) with internal teeth. The external gear drives the internal gear, meshing together inside the casing, causing fluid to be trapped and transported from the pump’s inlet to the outlet.

The choice between gear pumps and other pump types depends on several factors, including the specific application requirements, fluid properties, flow rates and pressures. It’s important to evaluate these factors and consult with a pump expert to determine the most suitable pump type for a particular application.

Take the following example of a Viking positive displacement pump, which clearly demonstrates how it works. Viking’s simple “gear-within a gear” principle has only twomoving parts. The first part is the positive displacement of the liquid that is accomplished by filling all the spaces completely between the teeth of the rotor and idler gears.

With every revolution of the pump shaft, a certain amount of the liquid enters the pump through the suction port. The liquid then goes on to fill the spaces between the teeth of the rotor and the idler. The crescent on the pump head then separates the flow of the liquid as it effortlessly moves toward the discharge port.

The idler gear, which carries the liquid between its teeth and the inside surface of the crescent, is then rotated on the pin, which is supported by the pump head. The rotor gear transports the liquid between its teeth, which travels between the casing and the outside surface of the crescent that is connected to the pump shaft. The four diagram drawings illustrated show how a positive displacement pump works.

Article courtesy of Kelair Pumps Australia, When Pump Knowledge Matters. Phone 1300 789 466, or visit

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