Plastic gears running in water - any experience anyone?

I have a design that requires a gear pinion to drive a larger geared component. The large component will have a gear ring on its outer
edge. The pinion can be of any material. To give an idea of scale, the pinion will be about 10mm in diameter and the larger gear about 50mm. Size of teeth etc not yet defined. The load is not great but the pinion speed will be up to about 1000rpm an an intermittent basis.
These parts need to run in water and the design dictates that alternatives i.e. sealing and providing grease lubrication are not possible.
Does anyone have experience of running gears in water like this?
All contributions welcomed,
Flyn
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Water is a useful slow speed lubricant. Clean water anyway. Dirty water is abrasive.
Brian W
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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
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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
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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.
F
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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
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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.
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Charly Coughran
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Why not justbuse a standard Mono-pump or something similar off the shelf?

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