Xref: utzoo sci.bio:4290 sci.chem:2945 sci.physics:16393
Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!apple!portal!cup.portal.com!mmm
From: mmm@cup.portal.com (Mark Robert Thorson)
Newsgroups: sci.bio,sci.chem,sci.physics
Subject: Fun With Vacuum Equipment
Message-ID: <38073@cup.portal.com>
Date: 15 Jan 91 23:38:30 GMT
Organization: The Portal System (TM)
Lines: 36

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.

Both pumps are Duo Seal brand from W. M. Welch.  They look to me like
sliding vane type pumps, probably single stage but possibly two.  Can
anyone familiar with this brand tell me more about it?

I want to do freeze-drying and perhaps make some aerogels.  I'm
concerned that overloading my vacuum chamber (8" x 8" x 12") might
put out too much vapor for the pump to handle.  Does anyone have
tips on how to avoid this situation?  My pumps have a sight glass
on both sides of the oil reservoir, so I think I might be able to
monitor the amount of water in the oil if I knew what to look for.

The sight glass has two lines, indicating an upper and lower level.
Is this like the maximum and minimum on a car engine dipstick?  Or
is it like the hot and cold marks on an automatic transmission dipstick?
Which line should I fill to, and do I do it after the machine has been
running or after it has been idle (running raises the oil level)?

Does anyone remember what year and/or month the Scientific American
article on aerogels appeared?

In case you're interested, I paid about $200 buying the vacuum chamber
(a Napco 5831) at auction, and $75 per pump from a local company that
was disposing of extra pumps from a large lot they had bought at a
different auction.