Comments on: The Gerotor Pump http://www.ret-monitor.com/articles/571/the-gerotor-pump/ Specific mission-critical info for professionals Fri, 18 May 2012 10:22:48 +0000 http://wordpress.org/?v=2.7.1 hourly 1 By: John Coxon http://www.ret-monitor.com/articles/571/the-gerotor-pump/comment-page-1/#comment-8959 John Coxon Mon, 12 Sep 2011 11:08:36 +0000 http://www.ret-monitor.com/articles/571/the-gerotor-pump/#comment-8959 Determining the flow rate of a gerotor pump is generally only one of simple geometry starting by subtracting the volume of the inner portion of the outer rotor from the volume of the outer portion of the inner rotor for each revolution. A positive displacement pump by definition the calculation is somewhat made slightly more complicated by the fact that the outer annulus of the pump has one more ‘tooth’ than the inner annulus. If you look very careful at such a pump in operating you will see that the inner annulus ‘teeth’ advance by one on the outer annulus after every rotation and so any calculation needs to take this into account. Thus the input shaft of a pump with 8 inner teeth will need to rotate 9 times to make the outer rotor rotate 8, the flow rate therefore will be proportionately less. I reality, clearance issues particularly at the tips of the ‘teeth’ will also introduce inefficiencies and so any actual flow rate will normally be slightly less than that calculated. If you are not up to doing the sort of mathematics required there are, I believe a number of commercial downloadable computer programmes that will assist you, some of which may even be free for the first few runs. For design engineers who don’t really want to re-invent the wheel, there are also companies who will supply only the inner and outer rotors and who have undertaken all this work themselves simply giving you the diameter of the outer rotor and the flow delivered per revolution of the inner rotor and leaving all the problems of deriving the precise profiles and manufacture to them. Unless you are going to make thousands of the same type of pump, this would normally be the preferred option. I hope this goes some way towards helping. Determining the flow rate of a gerotor pump is generally only one of simple geometry starting by subtracting the volume of the inner portion of the outer rotor from the volume of the outer portion of the inner rotor for each revolution. A positive displacement pump by definition the calculation is somewhat made slightly more complicated by the fact that the outer annulus of the pump has one more ‘tooth’ than the inner annulus. If you look very careful at such a pump in operating you will see that the inner annulus ‘teeth’ advance by one on the outer annulus after every rotation and so any calculation needs to take this into account. Thus the input shaft of a pump with 8 inner teeth will need to rotate 9 times to make the outer rotor rotate 8, the flow rate therefore will be proportionately less. I reality, clearance issues particularly at the tips of the ‘teeth’ will also introduce inefficiencies and so any actual flow rate will normally be slightly less than that calculated.

If you are not up to doing the sort of mathematics required there are, I believe a number of commercial downloadable computer programmes that will assist you, some of which may even be free for the first few runs.

For design engineers who don’t really want to re-invent the wheel, there are also companies who will supply only the inner and outer rotors and who have undertaken all this work themselves simply giving you the diameter of the outer rotor and the flow delivered per revolution of the inner rotor and leaving all the problems of deriving the precise profiles and manufacture to them. Unless you are going to make thousands of the same type of pump, this would normally be the preferred option.

I hope this goes some way towards helping.

]]> By: ulf sandberg http://www.ret-monitor.com/articles/571/the-gerotor-pump/comment-page-1/#comment-8938 ulf sandberg Wed, 07 Sep 2011 15:32:25 +0000 http://www.ret-monitor.com/articles/571/the-gerotor-pump/#comment-8938 Hi, I would need someone who could help me with the calculation of a the rotorset for a Gerotorpump. Any suggestions? Best regard Ulf Sandberg Hi,

I would need someone who could help me with the calculation of a the rotorset for a Gerotorpump.

Any suggestions?

Best regard

Ulf Sandberg

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