Plastic gears running in water - any experience anyone?

Water is a useful slow speed lubricant. Clean water anyway. Dirty water is abrasive.

Brian W

Many plastic gears are made of nylon resins. Nylons are hygroscopic enough to cause problems with swelling. Allow for this in the design or choose another material. Paul Mathews

Dear Flyn:

Gear pumps are used as positive displacement pumps in water applications. Wear on hardened steel is pretty high. Wear on plastic will be likely higher, even at this lower rpm rate. Be sure and leave clearance axially for the water to be ejected at lower pressures / speeds... might keep the erosion down if you are not trying to pump water.

Is the water at least clean?

David A. Smith

Thanks for the input from you all. The water is sea water and probably not very clean at all. It has occurred to me that the best option might be to make up a representative assembly, perhaps just using a couple of stock gears, and try it. That way I can do an accelerated life test.

Dear Flyn:

You are wise beyond your ears.

Really worthwhile to do a full analysis of failure, to see if the modes of failure can be identified... and perhaps controlled. Stay away from nylon.

What depth will these gears operate at? What life do you need from their function? ... I don't need to know, but you do.

David A. Smith

Flyn wrote in news: snipped-for-privacy@19g2000hsx.googlegroups.com:

I have made a number of marine underwater devices for a variety of tasks. The real problem is likely not going to be the gears, but the bearings. Seawater lubricated, filled teflon bearings with generous clearances and rubber sand exclusion seals work well.

Why not justbuse a standard Mono-pump or something similar off the shelf?