jim rozen wrote:
In article , Christopher Tidy says...


* Ask the seller what is has been used for. If it has been used in
industry for neon sign manufacture or air conditioning servicing it will
probably have seen much heavier use that if it was used in a school
science laboratory.

* If the seller has a vacuum gauge available, ask them to measure the
pump's ultimate vacuum.

* Inspect the oil. Is it dirty? Metallic particles in the oil may
indicate heavy pump wear. Vacuum pump oil is usually colourless and
doesn't smell. If it smells it's the wrong kind of oil.

* Unscrew the oil drain and let a few drops run out. Is the oil
contaminated with water?

* Listen to the pump running. These pumps are usually pretty quiet.
Clacking noises may indicate sticking vanes.


You missed the most important one: attempt to determine if the
pump has been used with any toxic substances in its former life.
This is hard to do, but some common tip-offs include:

Off-board oil filtration devices

Inert gas feed for purge or ballast

Residue around the intake or exhaust ports

Former owners include medical, or laser users

By all means, *ask* what the pump was used for, and ask
who owned it before the present owner, if that information
is available. Any fishy answers would be grounds for
me to pass on the item.

Good point Jim. I should have remembered that one!

Chris