Page 142 - Fluid Power Engineering

116 Cha pte r F o u r

FIGURE 4.27 Flow characteristics of typical internal gear pumps of different
sizes at 1450 rpm speed. (Courtesy of Bosch Rexroth AG.)

FIGURE 4.28
Construction of a
Gerotor pump.
(Courtesy of Bosch
Rexroth AG.)

gear (2), in the same direction of rotation. This is similar to the inter-
nal gear pump with a crescent seal.
The drive gear has one less tooth than the outer, driven, element.
The pumping chambers are formed by the adjacent pairs of teeth,
which are constantly in contact with the outer element, except for
clearance. As the rotor is turned, its gear tips are accurately machined
so they precisely follow the inner surface of the outer element. The
expanding chambers are created as the gear teeth withdraw. The
chamber reaches its maximum size when the female tooth of the out-
er rotor reaches the top dead center. During the second half of the
revolution, the spaces collapse, displacing the fluid to the outlet port,