[time-nuts] Maser info (vacuum levels)

Heathkid heathkid at heathkid.com
Fri Sep 3 04:53:11 UTC 2010

Surplus (free to good home table)?  Try finding someone who works with these 
pumps every day who will even part with an OLD pump (even if it doesn't 
work) just because... a broken spare is better than not having anything at 
all.  ;)

----- Original Message ----- 
From: "jimlux" <jimlux at earthlink.net>
To: <jfor at quik.com>; "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Friday, September 03, 2010 12:45 AM
Subject: Re: [time-nuts] Maser info (vacuum levels)

> J. Forster wrote:
>> Two things helped a lot:  Big pumps and an LN2 cold trap.
>> The LN2 trap (as long as it is kept filled) will condense most everything
>> except a few "permanent" gases. It also stops the backflow of pump oil.
>> However, if something goes wrong, you would not believe the mess.
>> A technician that worked for me years ago told of a vacuum chamber that
>> was used to test some Apollo instruments, maybe 6' long and 5' diameter
>> with a pair of 18" - 24" oil diff pumps.
> Yep, that sounds pretty typical for our thermal vacuum test setups..
> (JPL has some bigger chambers.. 25 foot with a solar simulator, for 
> instance).
> The one I like is the RF test chamber.. a 6 foot bell jar in an anechoic 
> chamber for testing antennas under high power.. I think that one has a 3 
> foot diameter aperture to the pump (52,000 liters/second.. yes indeed that 
> is a *fast* pump).
> http://mesa.jpl.nasa.gov/Vacuum_Breakdown_Facility/
> Actually, it's kind of interesting at the lab because there's all this old 
> stuff not being used anymore (giant roots roughing pumps), but it's still 
> connected up to the walls, even if the insides of the lab has had the 
> chamber removed.  It's probably more expensive to remove the pumps and 
> dispose of them as surplus than it is to just leave them in place (where 
> they've probably been since the 60s).  I do know that getting rid of an 
> old small pump is a huge pain.. someone has to come and certify it as not 
> being hazardous, and then they take it to some disposal facility, and then 
> it has to be listed for recovery, and some scrap dealer bids on it 
> (probably as a lot weighing a ton or more)  (e.g. no dumpster diving for 
> employees..)
>> One night the AC power went off and the emergency sequence failed. The
>> diff pump oil was sucked back into the system. It took them weeks to take
>> the whole thing appart, clean everything (think 55 gallon drums of
>> Trichlor) and get it back together.
> Oh yes... venting the chamber when the pump is hot is a BIG no-no..
> Even moreso when there's hardware under test in the chamber.  (we had a 
> piece of gear going through thermal vac with a cold plate using a glycol 
> loop to the chiller.. and the glycol leaked..)
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