leakage through the seal

[eduvillela]

Hello,

Here in my company we design and manufacture small pumps, among other equipments.
But we're having troubles with the pump sealing. After one year of running, the fluid (usually water - 86°F) starts to leak through the rubber seal. After disassembling the pump to fix the problem, we find out that the rubber seal reamins perfect and the shaft got damaged in the region where its worn by the rubber lip.

I suspect there might be an high eccentricity between the shaft and the rubber seal, or the pump shaft material (AISI 304) is too soft for this application. I'm thinking about changig it from AISI 304 to a martensitic stainless steel ( AISI 410, 420), which is harder.

What would you suggest?

Thank you

 

[wormandwheel]

Hi,

Have you any suspended solids in the system?
May be worth installing a particle filter if this is practical.

Additionally a different material seal? Maybe
Otherwise I would second trying a harder material

 

[Artisi]

A few photo's might help in receiving meaningful input to your problem.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[1gibson]

If you go from 304 to 410 (higher strength) maybe you can include a replaceable sleeve o-ringed to a smaller diameter shaft.

 

[EdStainless]

The rubber itself will be slightly abrasive because of the fillers in it.
304 is too soft for reliable shafts unless it has been cold drawn to increase its strength and hardness.
It is common to use 304 for a shaft with a small replaceable sleeve of 420 installed. Then when there is damage you can replace the seal and the sealing surface easily.

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P.E. Metallurgy, Plymouth Tube

 

[eduvillela]

There are no suspended solids in the system. It's simply water.

Perhaps a hard sleeve o-ringed might solve the problem, and it´s a pretty simple solution.
Another solution I've been thinking about is nitriding the shaft surface. So the hardness increases and the excessive wearing stops.

 

[EdStainless]

I have seen rubber lip seals cur into hardened material over time, which is why I like a replaceable running surface.
Localized hardening of the SS will raise the cost, and when the seal is replace you may have to replace the entire shaft.

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P.E. Metallurgy, Plymouth Tube

 

[eduvillela]

I see your point EdStainless. I've studied more the issue and I think letting the rubber lips run over a shaft sleeve will be the best and cheapest solution. And at any time the sleeve gets worn out it can be replaceable.

Thank you

 

[samafa]

Eduvilella,


The same as EdStainless, use replaceable shaft-sleeve with harder incresed rather than change the shaft or maybe coating the shaft. Easy way, also economist.

 

[Artisi]

Design the sleeve so you can "end for end" it when it wears - double the life.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)