Page 143 - Fluid Power Engineering

Hydraulic Pumps 117

FIGURE 4.29
(a) A twin-gear
screw pump and
(b) a treble-gear
screw pump.
(Courtesy of Bosch
Rexroth AG.)

formed at the side plate. The geometric volume of the Gerotor pump
is given as follows:
(
V = bz A max − A min ) (4.41)
g
where b = Tooth height, m
z = Number of rotor teeth

4.6.11 Screw Pumps
In screw pumps (see Fig. 4.29), the displacement chamber is formed
between the threads and housing. The following is an expression for
the geometric volume of a twin-gear screw pump:

π ⎛ α sin 2 α ⎞
−
2
2
2
)
V = ( D − d s D ⎜ − ⎟ s (4.42)
g 4 ⎝ 2 2 ⎠
+
with cos( )α= Dd (4.43)
2 D
4.6.12 Vane Pumps
Construction and Operation
Figure 4.30 shows the construction of a fixed displacement vane
pump. The rotor (2) is driven by the shaft (1) and rotates inside the
stator ring (cam ring) (3). The vanes (4) are mounted into radial slots