Yuken Gear Pumps
These pumps operate with two gears engaged with each other and rotating to feed a hydraulic fluid from the suction area to the discharge area. They all have fixed (constant) displacement capacities. They are categorized into external and internal gear pumps; the internal type generally has smaller discharge pulsation and lower noise level than the other. The gear pumps are relatively resistant to working fluid contamination. Pumps operate at 20 to 25 MPa (2 901 to 3 626 psi) and offer a displacement of 100 cm3/rev (6.10 cu.in./rev) for the single type. Similar to vane pumps, double type gear pumps are easy to construct.
High pressure gear pumps often adopt involute gears, which allow highly accurate processing, bringing about high system operation efficiency. Contacting with each other at two points, the gears rotate to entrap oil in the engaging parts, resulting in vibration and noise, which are reduced by a groove on the side plate allowing the oil to escape. Some low pressure gear pumps use trochoid gears. Figures 2.17 and 2.18 show the external and internal gear pumps.
The displacement of external gear pumps is determined by a chamber between the neighboring gear teeth and the inner surface of the casing; the displacement of the internal gear pump is determined by a chamber between the external and internal gears and a dash board. The crescent-shaped dash board (filler piece) separates the suction and discharge areas. For both the types, the sides of the gear teeth are sealed with side plates. The high pressure external gear pumps have a movable side plate by which high pressure flow is led to the rear side to press against the gear and keep a suitable clearance.
Gear pumps consist of relatively simple parts. They offer high suction performance at a low cost and are used in various fields: forklifts, industrial platform vehicles, construction machines such as excavators and wheel loaders, and supporting pumps for primary pumps. Compact packages containing the gear pump, safety and check valves, oil reservoir, and DC motor are popular in automobiles.
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