Positive displacement pumps are one of the most commonly used pump types in the industry. They displace a known quantity of liquid with each revolution of the pumping elements. This is done by trapping liquid between the pumping elements and a stationary casing.

As a type of positive displacement pump, external gear pumps are known for their simplicity, compact design, and reliability. They operate with a pumping action akin to internal gear pumps, where two gears come in to and out of mesh to generate flow. However, the distinctive feature of an external gear pump is the use of two identical gears rotating against each other; one gear is powered by a motor, transmitting motion to the second gear. Each gear is supported by a shaft with bearings on both sides of the gear.

Take the following example of a Viking external gear pump, which clearly demonstrates how it works:

1. As the gears come out of mesh, they create expanding volume on the inlet side of the pump. Liquid flows into the cavity and is trapped by the gear teeth as they rotate

2. Liquid travels around the interior of the casing in the pockets between the teeth and the casing – it does not pass between the gears

3. Finally, the meshing of the gears forces liquid through the outlet port under pressure

External gear pumps are used in various industries for low-to-medium pressure applications including acids and caustic, chemical mixing and blending, various fuel oils and lube oils, alcohols and solvents, as well as industrial, agricultural, and mobile hydraulic applications

Selecting the appropriate pump type, whether it be gear pumps or alternatives, relies on various considerations such as the unique demands of the application, fluid characteristics, and the required flow rates and pressures. A thorough assessment of these factors, coupled with expert advice from a pump specialist, is crucial to identify the optimal pump type for a given application.

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

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