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From: ghg@en.ecn.purdue.edu (George Goble)
Newsgroups: sci.bio,sci.chem,sci.physics
Subject: Re: Fun With Vacuum Equipment
Message-ID: <1991Jan16.121112.23208@en.ecn.purdue.edu>
Date: 16 Jan 91 12:11:12 GMT
References: <38073@cup.portal.com>
Organization: Purdue University Engineering Computer Network
Lines: 32

In article <38073@cup.portal.com> mmm@cup.portal.com (Mark Robert Thorson) writes:
>I just acquired a vacuum oven and two old (but working) vacuum pumps,
>and I've got a few questions about using the equipment.
>
>First, I changed the old oil because I was afraid it might be crap.
>I replaced it with 30 weight single-viscosity non-detergent motor oil.
>It seems to work fine, but I was wondering whether this was a good
>idea (as opposed to buying oil specifically made for vacuum pumps).
>I'm not shooting for very high vacua -- I'd be happy achieving 10 um
>or even somewhat worse.  I'm mostly concerned with preserving the life
>of the equipment, and I plan to do frequent oil changes hence I want
>something cheap and readily available.

I have two Vac pumps (2 stage, vane). One is a "Robinair", the other is
a "J/B" (for refrigeration pumpdowns and dehydrating).  Each holds approx
16 oz of oil.  Motor oil (and compressor oil) "boils" at 250 microns or
higher.  Vac pump oil boils at less than 5 or 10 microns.  Refrigeration
pumps (two stage), can regularly achieve 40-50 micron (0 microns is 
"perfect"), if the oil is fresh.

I change the oil every use (or more)..  Running a pump, even for a few
seconds, will contaminate the oil enough to degrade it.

If one still has moisture in a system, the "blank off" (pump valved off)
vac will be around 1500 microns (one needs a micron gauge for this).

The Welch pumps in the dept here get their oil changed every 6 months or so,
but they just hold deep vac chambers for months on end, and dont ingest
moisture, etc, like refrigeration pumps do.

If you go to a refrigation wholesaler, vac pump oil is around $10/gal.
--ghg