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Posted by pv=nrt on January 7, 2007, 4:34 pm
Hi,
I was practicing my evacuation technique this afternoon using an old
empty CO2 cylinder. It led me to a couple questions:
1. I connected my digital micron guage to the blue fitting on my
manifold set and connected center directly to the pump. I pumped just
the micron guage itself down to 500 microns to test my setup. When I
shut the valve to isolate vacuum in the micron guage it gradualy rose
to something above 2000 microns. (my digital guage isn't capable of
measuring above 2000 microns). I thought the micron guage might have
a small leak at the fitting but I tested it with 150 psi Nitrogen and
there were no soap bubbles at the fitting or any other place in this
entire setup. My manifold set's analog vacuum guage has been
connected to it for hours and hasn't budged above 28-29 inchs HG so I
assume the micron guage really is airtight at the fitting. I assume
that it leveled out somewhere above 2000 microns. Does this sound
right?
2. I hooked up my empty CO2 bottle and pumped it down. The micron
guage gradually stair stepped it's way to 500 microns but on the way
down it would kind of oscillate. For example it would go to 1700
microns then go up to 2000 microns and then down to about 1600 microns
then up to about 1900 microns then back down again. Is this stair
step progression down to 500 microns a normal part of boiling off
condensates? It did seems like the magnitude of the ocsillations
decreased as I approached 500 microns.
3. Every book and manual states that 500 microns is the goal for a
complete evacuation. However doesn't it need to be adjusted based on
elevation? For example I'm at 1300 ft above sea level. Shouldn't my
goal be approx. 800 microns. (ie about 1" per 1000 ft ignoring the
minor barometric differences.)
4. Modern Refrigeration and the other books I'm reading seem to say
that either deep vacuum to 500 microns or triple evacation are the two
methods. However which is more effective ignoring the time element?
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