Hydraulics - Seafish

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In this pump both gears rotate in the same direction but, instead
of a crescent shaped seal, the gears are so designed that the tips
of the teeth of the internal gear are always in contact with the
profile of the external gear and so form a seal.
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The inner gear has one tooth less than the external gear.
In each of the gear pumps shown in Figures 38,39 and 40 the tips
of the teeth form the seal. Since all moving parts must have some
form of clearance in order to allow them to operate, this seal is
not perfect and there is always a little leakage, and therefore, a
small loss in pressure and flow.
To reduce this leakage, end plates are fitted to the sides of the
gears and the clearance kept as small as practicable. In the pump
casing the ports are arranged so that the inlet port is at the point
where the teeth come out of mesh, and the delivery port at the
point where the teeth mesh together.
To obtain high pressure these pumps may be mounted in a
common body and the outlet from one pump led to the inlet of
the next, the pressure being built up stage by stage.
Wear on the teeth or casing will increase leakage and after
long service, the pump will require replacing.
Vane Pumps
In Segment One the two basic forms of vane pump were also
shown. In a vane pump, a rotor with longitudinal slots is driven
by a driveshaft between closely fitting side plates inside a
circular or elliptical ring. The vanes, which are hardened and
polished, slide in and out of the slots to maintain contact with the
surface of the casing and make a seal.
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