Need basic design review

[platteriver]

I paid a firm to design a gear pump for me and I am REALLY skeptical about the design. I am not a mechanical engineer and am hoping you guys could give me some basic input.

This is a very small gear pump similar to a chemical spray pump. It is running off of a 9.6v battery and a small motor with an RPM of 5700 under load at max efficiency. The motor shaft inserts thru the pump wall and directly into the drive gear
(pinion gear). No bushing. A lip seal is in place to prevent leaks. Neither the drive or the idler have any shaft, bushing, or other means of stabilization other than the recessed portion of the housing.Gear side housing uses a recessed o-ring to seal. The other half of the housing is completly flat. Whole thing is machined out of delrin

The gears are binding repeatedly and the drive gear is showing tremendous wear. Almost like grooves cut into it on a lathe.

Specific questions- shouldn't it have some sort of bushing or "peg " to hold the gears? or the drive shaft?
In similar designs I have seen the lip seal in place past the bushing, this one is simply around the shaft and fits into the bowl. Is this right?
Finally, the first submitted prototype didn't produce enough flow so they increased the size of the gears and the output port, but left the intake the exact same size. ?? This has to be a mistake right??

are there any resouces that detail design requirements and effects of gear pumps?

Thanks in advance for any help your community can provide.

 

[MikeHalloran]

I've destroyed and rebuilt a few gear pumps, and I've never seen one without some kind of pin/hub/shaft/bushing or some kind of radial bearing, other than the gear tooth tips, locating the gears. The drive shaft is commonly used to support one gear. The idler gear definitely needs a pin or bearing or something. The other details you mentioned may or may not be kosher.

Binding is not a good sign.

I'm not aware of a book that tells you how to design the internal details of a gear pump. I assume that pump manufacturers have design standards, and I assume they're proprietary.
Comparative anatomy is all that remains.

This might be a good time to buy a pump from Grainger, and see how it differs from the one designed for you. Of course the sizes will be different; it's the topology you care about in this case.









Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

There should be some sort of feature to align the motor to the drive gear. Depending on how long the motor shaft is, there may need to be a bushing where the shaft enters the housing. This would also keep the shaft centered in the seal.
There should be a shaft/pin for the idler to maintain gear center distance.
Scoring on the sides of the gear is due to debris or poor machining.
What is the gear material? What is the operating pressure? What is the fluid being pumped?
Without support the gears will be pushed into the walls of the gear chambers binding the pump.

Ted

 

[EdDanzer]

There could be many problems with the design. The fluid, the pressure and the speed can all cause problems with the best design. Providing more information about pressure, fluid, size and pictures of the failed parts will help provide more accurate information.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[racookpe1978]

Show an image of their design, please.