Positive displacement gear pumps are used to pump thick and viscous fluids without suspended solids, at low and high temperature. Thanks to the volumetric effect of the gear, they are always self-priming with good suction characteristics; they have also a constant flow even if delivery pressure changes during operation. Internal fine tolerances make these pumps usable only with clean fluids having some lubrication properties.
Typical application of gear pumps are machinery/engine lubrication, hydraulic power units, chemical additive metering, foam blending in fire-fighting system, fuel oil supply or booster and general transfer of viscous liquids as glue, paints, grease and so on.
These pumps use two identical gears rotating against each other: the drive gear operates the idler gear. Liquid flows into the cavity of the teeth and is directed and pressurized toward the discharge port by the gear rotation. Each gear is fitted on a shaft supported by two internal bushings immersed in the pumped liquid. Thanks to the rigidity of the shafts, the fine tolerance between rotating parts and the improved gear profile, pumps have quite operation and low noise. Moerover as there are no external ball bearings, pump has only one shaft penetration through the housing sealed with a mechanical seal. Materials of internal parts, like gear, shaft, gaskets and mechanical seal are selected according to the pumped fluid. Pumps are usually driven with electric motors through elastic coupling but it is possible also to use pneumatic or hydraulic motors.