A type of positive displacement pump consisting of gears with meshing teeth (see Fig. 52). The rate of flow is determined by the number and size of the spaces between the teeth and their rotational speed. A close tolerance is required between the teeth to prevent leakage, although unlike the reciprocating type pump, check valves are not required. They require liquids with good lubricating properties and are unsuitable for fluids with abrasive properties.

Fig. 52 Gear-type rotary pump