Rotary gear pump for vacuum

[Rich Feldman]

Couple years ago I reported a flea market item dragged home on a rainy day: a Welch 8890 "GEM 1.0" vacuum pump.
Unfortunately the product did not suck, although the motor ran fine.
Internet taught me that it's a two-stage rotary gear pump instead of vane pump. Like oil pumps in many engines (pictured).

gerotor.JPG (21.97 KiB) Viewed 2921 times

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Designed to run 24/7 for things like evaporators in chem labs. Ultimate vacuum rating is only 0.1 torr, but there's less friction/wear/power than vane pumps of similar displacement.

Yesterday it was time to find out why it didn't work. Removing motor showed that the shaft coupling was literally broken!
I couldn't turn the shaft on the pump side, so drained the oil (almost nothing came out) and opened up the oil box.
Surprised how much oil spilled out when the gasket seal was broken. Oh, because the drain port was literally clogged.
This might be a candidate for cruddiest vacuum pump contest. At bottom is broken steel part of the Lovejoy coupling.

I figure it deserves a bit of effort to get the moving parts freed up. Not too much work -- the overhaul kit with gaskets, shaft seals, o-rings etc costs $120,
and I have a couple of rotary vane pumps that work better than this ever did.

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Scraping encrustations from the aluminum end plate which bears the pump body, I found a place corroded all the way through to the shaft-coupling space.
Am hoping the icky stuff isn't too horribly leap-out-and-get-you toxic.

[Richard Hull]

Belongs in a land fill.

Richard Hull

[John Futter]

only if you want to poison a cubic mile of earth

[Rich Feldman]

I suffer from an affliction called duty to stuff.
Spent more than an hour unsticking and cleaning up the pump core; now it can be turned freely with fingertips on oily shaft.
With clear plastic sheet ends, it would make a nice artifact for show-and-tell.

This pic also shows the pitting of aluminum plate due to chemical activity of something that got pumped.
I have seen no pitting to speak of on any steel parts.

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Now hoping to follow Richard's advice and don't waste more time trying to restore actual pump functionality.
Things like check valve reeds, shaft oil seal, oil box gasket, chemical perforation, and of course the broken shaft coupling aren't worth dealing with.

[Rich Feldman]

Lest there be any doubt, behold the head of my enemy.

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These parts are being saved for a while, which is probably more than they deserve.

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The motor (visible in OP), with handle and cord and switch, will go to August 8 flea market if that happens.
Otherwise goes into the transformers-and-motors scrap bin.

[Dennis P Brown]

Applaud your effort and determination. And sorry your efforts didn't pan out. Unfortunately, the waste from the cleaning process is now added to the waste of the pump. Sometimes best to not try and salvage extreme cases like that.

I stopped buying two stage mechanical pumps seven years ago because they all worked to spec's, were dirt cheap and I realized I didn't need more (two primaries and a backup) - so I passed on two or three more. Searching ebay was very useful - I paid $10 for each - shipping was the most expensive part and that was like $30. I guess such finds are getting rare now but it is possible to get very good pumps rather than scrap and still pay little.