Re: Yet more: diffusion pumps

To: neon-l@netcom.com
Subject: Re: Yet more: diffusion pumps
From: dead@netcom.com (John Anderson)
Date: Sun, 4 Feb 1996 10:46:01 -0600
Reply-To: neon-l@netcom.com
Sender: owner-neon-l@netcom.com
>At 10:07 AM 2/1/96 -1000, you wrote:
>> >I do believe there some point of decreasing returns.
>>
>>
>>
>How bout some increasing returns.....In all the diagrams for pumping &
>bombarding setups I fail to see vacume traps in the systems.  I was a
>chemistry major in college and worked for three years doing reasearch
>in organo-metallic chemistry.  In my reasearch I had to perform reactions
>in either a vacume or in an inert (and bone dry) atmosphere of argon.  I
>learned how to make vacume manifolds (with the old silicone grease stopcocks)
>out of pyrex.  I made alot of vacume traps, we allways had one in-line (before)
>the vacume pump to trap any liquid's like acetone, water, benzene etc.  The


Mike,

That is a good point.  I started hot-glass work as a scientific
glassblower, and was at one point under the impression that all HV systems
had cold traps.  There was a system (much like a neon manifold) we used to
pump out dewars after silvering the inside.  There was a cold trap between
the diffusion pump and mechanical pump (a welch 1402) and between the dif
pump and the manifold.  Filling the 2nd trap with liquid N2 immediately
dropped the pressure several DECADES (as in 10-4  to  10-7or8).  Both
pumps' oil remained crystal clear too.

I think the neon industry may be one of the few users of HV technology that
doesn't use cold traps.  I've thought about making one use with neon -
liquid N2 would undoubtedly clean a dirty mercury tube nicely.  But then
again do I really want to get into this arena of the business?

You can buy liquid N2 here in town by the liter - bring in a thermos bottle
with a vent drilled into the top.  It will keep very long in one of these
(several days), and it's not very expensive.  Neon processing could use the
simplest of traps:

                                      out (to manifold)
                                |  |
                               _|  |_
                              | |  | |____
                              | |  |         in (from unit)
                              | |  |  ____
                              | |  | |
                            | | |  | | |
                            | | |  | | |
                            | | |  | | |
                            | | |  | | | --- dewar (thermos) to hold cold stuff
                            | | |  | | |
                            | | |  | | |
                            | | |  | | |
                            | | |  | | |
                            | |______| |
                            |__________|


I'm a bad example to follow on neon equipment, having a tendency towards
the outrageous.  Fortunately, my wife usually tags along when I go to
auctions here from semiconductor fab plants!

   -John