5.1.3 External gear pumps
External gear pumps mainly consist of the friction bearing mounted
gear pair and the housing with front and rear covers. The drive
shaft, which is sealed with a radial seal, protrudes from the front
cover. The bearing forces are absorbed by friction bearings. These
have been designed for high pressures and have excellent antifric-
tion properties - particularly at low speeds. The gears have 12
teeth each. This keeps flow pulses and noise emissions at a low
level.
Fig. 84: Axial compensation of gear pump
1
Axial seal
5
Cover
2
Outer pressure field
6
Flange
3
Inner pressure field
7
Sealing zone
4
Radial seal
8
Compensation forces
Internal sealing of the pressure chambers is achieved by flow
volume dependent forces. This results in an excellent rate of effi-
ciency. On the rear side the moveable bearing bushings are pres-
surized and thus tightly pressed against the gears. The pressurized
pressure fields are thereby limited by special seals. Sealing around
the circumference of the gears to the housing is assured by small
gaps, which appears between gears and housing in dependence
on the pressure.
Hydraulic system – Basic principles
BW 900-50
101
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