In brief
A gear pump is a positive displacement pump in which two meshing gears carry liquid in the tooth gaps from the suction side to the discharge side.
Contents
What is Gear pump?
As the gears rotate, tooth gaps open on the suction side, fill with liquid and carry it along the housing wall to the discharge side, where the meshing of the teeth displaces it. Gear pumps are simple, robust and inexpensive and are used as fixed displacement pumps in hydraulic power units, as lubricating oil pumps and as transfer pumps for viscous media such as oils, resins or adhesives.
In the external gear pump, two externally toothed gears mesh; in the internal gear pump, an externally toothed pinion runs inside an internally toothed ring gear, which is quieter and produces less pulsation. Key parameters are displacement per revolution, speed range, maximum pressure, direction of rotation, shaft end and mounting flange. Because the displacement is fixed by design, the flow rate is varied via the speed.
Wear on tooth flanks, bearings and side plates enlarges the internal clearances, so efficiency drops. Causes are dirt particles, cavitation due to excessive suction resistance and dry running. Because of their simple design, gear pumps are often replaced completely rather than repaired when worn. For critical hydraulic power units, it is worth keeping a suitable pump in reserve.
In practice: maintenance and procurement
For a replacement, the displacement, direction of rotation, shaft end, flange, connection type and maximum pressure are needed. With gear pumps in particular, the direction of rotation is crucial, because many versions may only be operated in one direction.
Synonyms and abbreviations: external gear pump · internal gear pump · fixed displacement pump · gear-type pump
Frequently asked questions
What is the difference between an external and an internal gear pump?
In an external gear pump, two externally toothed gears mesh; it is simple and inexpensive but comparatively noisy. In an internal gear pump, a pinion rotates inside an internally toothed ring gear, separated by a crescent-shaped filler piece. It runs more quietly and with less pulsation and is therefore often chosen for noise-sensitive applications.
How do you identify the direction of rotation of a gear pump?
The direction of rotation is stated looking at the shaft end, i.e. clockwise or anticlockwise. It is given in the type designation or marked by an arrow on the housing. Different-sized ports often also reveal the suction and discharge sides. A pump installed the wrong way round will not deliver or will be damaged.
What information is needed to replace a gear pump?
Required are the displacement in cubic centimetres per revolution, maximum operating pressure, direction of rotation, shaft form, mounting flange, position and type of ports and speed range. For process pumps, the pumped medium, viscosity, temperature, materials and shaft seal are also needed. The nameplate and manufacturer part number speed up identification.
Why is a gear pump getting noisy?
Increased noise often indicates cavitation due to excessive suction resistance, oil that is too viscous when cold, or air being drawn in through leaking suction lines. Worn bearings and tooth flanks or incorrect alignment with the drive shaft also generate noise. Checking the suction side is often the first step.