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What's A Gerotor?
Operating Principle
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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 installation.

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 oil viscosity.

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 inch.

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 gerotors.

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 tolerance.

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.

 
Home | What's A Gerotor? | Operating Principle | Gerotor History | Suggested Uses | Gerotor Sizing | Pictures | Contact Us 10/12/2004