BOOK IN SERIES
HYDRAULICS
in Industrial and Mobile Applications
CHAPTER 4
OIL HYDRAULIC PUMPS
Get your copy of this book :
http://www.assofluid.it/en/publications-requestt
Gerotor pumps
the second half the space shrinks progressively and oil can
be driver into the outlet. Obviously the same cycle occurs as
each tooth alternates: after 1/6 of revolution tooth 2 meshes
with B, then 3 meshes with C and so on.
Figure 4.19
(Figure 4.18).
Gerotor pumps consist of a central (external-toothed) male
gear, solidly connected to the transmission shaft and an
internal-toothed (female) gear that can revolve and that is
held only on the seat of the pump housing. The internal male
gear (usually made up of not more than 6-8 teeth) always has
one less tooth than the peripheral female gear; for instance,
if an internal male gear (the real Gerotor) has six external
teeth, the gearwheel will have seven internal teeth. This is
why a specific Gerotor tooth meshes with its corresponding
internal tooth of the female gear of the external wheel only
once during the whole revolution.
Assume the pump is revolving and tooth 1 of the Gero tor is
fully engaged with the internal tooth A (Figure 4.18). During
the first half of the revolution, since the female gear has
larger teeth, a wider and wider space originates between the
gears resulting in the vacuum needed during suction. During
60
Global MDA Journal may 2018
Gerotor pumps cause little noise, need almost no
maintenance, are light and quite small, have little pulsating
flow, few components and an easy and compact casing. They
are suitable for revolutions ranging between 500 and 3500
rpm, their volumetric efficiency is low but adequate for the
specific functions and the recommended viscosity range is
20-180 cSt. Since Gerotor pumps cannot sustain more than
50 รท 70 bar, they are confined to lubrication circuits and to
serve as booster pumps directly mounted on the main pump
(Figure 4.19).
Some of the newest pumps, which are still at an experimental
stage, managed to reach working pressures above 150 bar
with an overall efficiency of 75% thanks to the enhanced
compensation of the axial play. Another interesting pump
that is similar to a Gerotor pump under some respects but
that cannot be classified as Gerotor (it has more standard-
shaped teeth) has long been available and it is employed in
many applications.