Gear Pump Design Guides? 4

[afafafy]

Hi. I've been asked to design an external Gear Pump from scratch. I've found the basic information about how the pumps work, but haven't found a "plug in the the volume output you want, and out pops the gear sizing" type of information. (I'm rusty on my gear design skills, so it may be my fault...) I've been given a flow rate to meet, and have been requested to minimize the volume that the pump takes up. Any help would be appreciated.

 

[FACS]

It's probably best if you do this from scratch, and not use a plug and chug. I say this because you need to learn a few things as you go.

We don't know what your volumes are so I am going to write a generic procedure. You can Email me questions later. I've designed many positive displacement pumps from scratch.

1) You need to draw a gear. Start with the easy; Use a solid model CAD to draw an involuted gear tooth. If you need help on how to do this, let me know.

Understand that your volumetric calculations are only going to be ball-park. There are many factors that will determine the actual output. You need to remember during your design, that you may have to make your gear set longer or shorter to hit your target. Be sure to leave room in your housing to lengthen or shorten the gear set.

2) Once you have two gear teeth modeled, measure the surface area with the CAD measurement tools. Measure only one side of each tooth, the area that the fluid will occupy. From the centerline of one tooth to the centerline of the other tooth.

3) Measure the arc length from the centerlines. The tip path.

4) Calculate the volume.

5) Determine the RPMs and see how close you are.

6) Need more? Lengthen the gear set; Need less? Shorten the gear set.

7) Now, if you are way off, select another gear set to model.

It may take you a while to draw your first set of gears, once you get the hang of it, you will have a library of gear sets. You will probably be able to go from 0-3 gpm with one gear set; But, after that you may need to go to larger gears for more volume, lengthening and shortening the gears as you go.

It's a game of long small diameter gears and short large diameter gears.

Once you have a gear set designed, it's time to make the housing.

Then we talk about slip, seals, tolerances, material.

Charlie

http://www.facsco.com

 

[enirwin]

You can estimate spur gear pump flow with the following formula. This will allow you to run through some sizing options before starting gear design.

G=(N*W*C*(D-C))/73.48

G=pump flow(gpm)
N=speed (rpm)
W=gear face width (inches)
C=center distance between gears (inches)
D=gear OD (inches).

This is from a very old Design News article. You will need to apply an appropriate volumetric efficiency to account for internal leakage.