Suggestions for using Gerotor Elements
1. Gerotor Pump Elements should be used in sets as
received from the factory.
2. Gerotor Elements are manufactured with close
dimensional control and require similar controls in their
3. The following tolerances can be used as a guide
to insure good performance and life.
Eccentricity: i.e.: distance between center around
which the outer member rotates and the center of rotation of the inner
member to be as shown, +/-. 0005 inch.
Side Clearance: i.e.: difference between gerotor
thickness (inner and outer are the same) and the depth of recess
gerotor runs in is .0015" to .003" for moderate pressures, speeds and
Running Clearance: i.e.: difference in diameter
between outer gerotor member and recess .002 to .004 inch.
Bearing alignment: The bearings should be in line
with each other and square with the gerotor cavity within .0005' per
Housing Clearance: zero to .002 maximum over
eccentric ring O.D.
4. Eccentric rings: An eccentric ring with correct
eccentricity, side clearance and running clearance is available as a
third piece of each gerotor set. Its use eliminates difficult
machining operations, all boring and turning then are concentric and
to normal machining tolerances. In addition, accurate bearing
alignment can be assured by piloting the housings on the O.D. of the
eccentric ring. Proper side clearance is assured by bolting up tight
against the eccentric ring which is the proper amount thicker than the
5. Surface Finishes: The sides of the recess should
be flat and at least 64 RMS in smoothness. The outside diameter of the
recess should be at least 64 RMS and the corners must be perfectly
sharp or undercut slightly to insure noninterference with the corners
of the outer gerotor.
6. Bearings: may be anti friction or sleeve type and
sized according to good engineering practice. When using sleeve
bearings, pressed in place, we urge final sizing be accomplished by
boring rather than reaming, to insure maintaining eccentricity
7. Shafting: As the inner and outer gerotor members
are held in, correct running position by the O.D. of the recess and
the shaft, the latter should be reasonably sturdy and free from
deflection. Preferred construction is a hardened shaft ground .0005 to
.0015 free in the inner gerotor bore.
8. Driving: between shaft and gerotor can be
accomplished by key, spline or press fit. However, the last two are
second choice. If a press fit must be used, we must know how much the
press is and have the gerotor sets especially manufactured to maintain
proper fit. Splines ~ are expensive and will not locate the inner
gerotor properly unless made with minimum radial freedom. We recommend
a key drive, or, in very small sizes, a cross pin works well. Multiple
keys can be used, although usually not necessary. The shaft may be
driven by a coupling spline, or gear, etc. It may be positioned
axially by use of snap rings on the shaft either side of the inner
gerotor, which can take a reasonable amount of end thrust.
9. Porting: Porting should be in accordance, with
that shown in "Suggested Port Configuration" (p. 4). These ports are
suitable for rotation in either direction.
10. Line Size: We recommend particular attention is
paid to providing adequate line size. Page 4 lists acceptable sizes
for various capacities. Inlet oil velocities of about 4'/see. Will
permit satisfactory performance. The long inlet cycle of the gerotor
makes for high pumping efficiency, but line sizes must be sufficient
to permit complete filling; otherwise, cavitation, loss of efficiency,
and possible damage to the elements may occur.
11. Pump Housing: We recommend the two halves of the
pump housing be positioned together with a pilot. Doweling can be used
if great care is taken to insure concentricity of bearings and proper
eccentricity of gerotor recess. The parts of the housing in contact
with the gerotor can be made of cast iron, anodized aluminum, bronze
or other material having good bearing characteristics.
REVERSIBILITY FEATURE Changing the direction of
rotation of a gerotor pump changes the direction of flow. Changing the
eccentricity of a gerotor pump 180° also reverses flow. If
eccentricity is changed 180° with each reversal of rotation, direction
of flow will remain unchanged. This is accomplished by using a free
turning eccentric ring with stop pin in housing to limit rotation of
180° either way. A simple Friction drive between outer rotor and
eccentric ring assures proper positioning of the ring to maintain
direction of flow unchanged regardless of drive direction reversals.