The 30 Hg is the height in inches of a column of mercury supported by
the vacuum (980 millimeters, for you metric buffs, , IIRC) - NOT the
weight in pounds. That corresponds to 14.7 lbs per square inch (sea
level, normal temperature). You can't do better than 1 atmosphere of
vacuum, even in outer space!
On the other hand, for outgassing resin, you don't need near perfect
vacuum; even a 5 pound vacuum will draw out lots of bubbles. Just use a
less viscous resin mix, or pump longer. Also, periodically relieving
the vacuum and then pumping some more seems to help.
Norm
rruss45826@... wrote:
>
>In a message dated 5/6/2005 1:21:48 A.M. Eastern Daylight Time,
>robert.hedan@... writes:
>
>How can you pull the vacuum down 2 atmospheres? Assuming I am at 1
>atmosphere, isn't 0 a vacuum? Or did I miss something and you can a bigger
>vacuum? Huh? How can you go to negative atmosphere? I thought atmospheres
>were mostly used for pressure chambers.
>
>I often see reference to 0-30Hg for vacuum chambers, something about mercury
>level. I figure I'll see where the vacuum dial sits at rest, and where it
>goes as air is pumped out is the vacuum side.
>
>Robert
>:)
>
>
>
>Most vacuum is measured in HG which is mercury. being so heavy you can use a
>much smaller scale! Now if I remember my old school books normal atmosphere
>at sea level is about 15lb's per sq inch. Now 2 Ats. would be 30lbs per sq
>inch. No go to vacuum and the same applies but in the opposite. So 30HG vacuum
>would be 2 Ats. When I do A/C work this is the standard test we do. Draw down
>to as close to -30 hg and cap it off. wait 1 hour and see if we have any
>leaks then charge the system.
>If I did not get any of the math right I am sure someone will jump in and
>correct it! High school was a long time ago! LOL
>Just putting the mold under 1 At or -15lbs of vacuum will do the job you
>need to do!
>
>Ray Russell
>NMRA-40609
>General Contractor
>Norfolk & Western Railroad
>Pocahontas Division
>Circa 1958
>Visit The "NEW" Pocahontas Website at:_ Click here: N & W Pocahontas
>Division_ (http://members.aol.com/rruss45826/public_html/index.html)
>http://members.aol.com/rruss45826/public_html/index.html
>
>OR_ Click here: Pocahontas Home_
>(http://milliron.home.sprynet.com/Pocahontas/Pocahontas1.htm)
>For the old website!
>http://milliron.home.sprynet.com/Pocahontas/Pocahontas1.htm
>
>
>[Non-text portions of this message have been removed]
>
>
>
>
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>
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