Wayde Allen (wallen@boulder.nist.gov)
Thu, 27 May 1999 14:39:27 -0600 (MDT)
On Thu, 27 May 1999, John Melanson wrote:
> Somewhere (an ancient Scientific American "Amateur Scientist", maybe) I
> remember reading about using a refrigerator pump for a rather high vacuum,
> but thought you had to do something about feeding it oil. Do you know about
> that?
It sounds like what you are talking about is a diffusion pump since you
mention high vacuum. These work by creating flow of low vapor pressure
oil (or liquid mercury) between several chambers. Any gas molecules
remaining in the already existing vacuum get pulled along by the oil or
mercury stream. You can get very high vacuums this way, but you have to
pull a fairly good vacuum first using more traditional means (piston
pumps, etc.). You also often have to use a cryo-trap to condense the
little bit of oil or mercury vapor that the diffusion pump releases into
the vacuum. I've used diffusion pumps for evacuating liquid helium
dewars, but it wouldn't work for a vacuum printing frame.
You really shouldn't need a very hard vacuum for a contact printing frame.
I'd guess that an old vacuum cleaner would work OK although the noise
could be a problem. Depending on the size of your vacuum frame and how
much it leaks, the aspirator for a vacuum filtration system would probably
work too. It could also serve dual purpose for filtering your chemistry.
Finally, I've seen refrigerator compressors used to create modest vacuums.
To the best of my knowledge there was no lubrication problem, but is worth
looking into.
- Wayde
(wallen@boulder.nist.gov)
This archive was generated by hypermail 2.0b3 on Thu Oct 28 1999 - 21:39:35