Gerotor Pump Harmonics
Gerotor Pump Harmonics
(OP)
I'm looking for insight into causes of higher order harmonics in the noise (and vibration) of a gerotor oil pump.
The inner gear has 9 teeth, so the fundamental pump frequency is too low to be an issue at the operating speed; but the 3rd, 4th, and 5th harmonics create an issue. The 3rd harmonic is the worst and varies greatly (>3 dB) among several units tested.
Any clues as to the mechanical or hydraulic reasons for such behavior would be appreciated.
Regards,
Tranny
The inner gear has 9 teeth, so the fundamental pump frequency is too low to be an issue at the operating speed; but the 3rd, 4th, and 5th harmonics create an issue. The 3rd harmonic is the worst and varies greatly (>3 dB) among several units tested.
Any clues as to the mechanical or hydraulic reasons for such behavior would be appreciated.
Regards,
Tranny





RE: Gerotor Pump Harmonics
Normally what they will suggest is that at 9x per revolution there is a sharp pulse, either mechanical impact or hydraulic pulse.
The pump is similar to a gear as you know. I would think improper backlash may create mechanical impacting as the tooth goes into the valley (sorry I don't know the correct terms).
We have one experience with these style pumps installed as aux oil pump for a large chiller. In that application they "frequently" (perhaps 5x over 10 years among 6 units) fracture they key or keyway such that the pump stops rotating. We suspect possibly some misalignment induced by pipe strain but we really don't know the root cause.
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RE: Gerotor Pump Harmonics
So, look at your hydraulic pressure patterns and see if they vary between pumps, failing that look at your clearances.
3 dB variation is damn good, actually.
Cheers
Greg Locock
RE: Gerotor Pump Harmonics
We'll look at those things
RE: Gerotor Pump Harmonics
So don't worry about it but it makes analysis more "interesting".
Ron Frend
http://www.predicon.net
RE: Gerotor Pump Harmonics
Yes I realize any pump will generate lots of harmonics...any advice on how to reduce their amplitudes (other than reducing the pump pressure pulsation amplitude)?
Thanks!
RE: Gerotor Pump Harmonics
I am looking for a way to reduce it. Any ideas about the porting geometry? I used Nichols Portland standard geometry and I was told that there is no better design possible.
Any comments? Apreciate you help. Thanks!
RE: Gerotor Pump Harmonics
All the Gerotor teeth I have ever seen are 'straight', i.e., not twisted like a helical gear. Straight cut gears also resemble the rotor of a mechanical siren. Which leads me to this; I haven't tried it, but it should be possible to reduce the noise from a gear pump with a little porting work, skewing the edge of the inlet port so it's not parallel to the gear teeth or the shaft. No such opportunity presents for a Gerotor.
Somebody with a CNC id/od grinder could probably produce one-off Gerotor sets with twisted teeth, or it could be done in quantity with powder metal, but is there a market for really quiet gear pumps?
Okay, there is, but the pumps are called screw pumps.
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA