Vacuum Info
Updated: October 20, 2004
Go to www.belljar.net and follow the link to "Vacuum on the Cheap".
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Original poster: Terry F.
Hi: Many cheap bicycle tire pumps can be modified by just reversing the
diaphragm and filling some empty spaces with putty. Put the reverse valve as
close as possible... Edmund Scientific sells those nice little hand
pumps too (don't bother with the gauge) which will, in time, pump a very good
vacuum. I have even sucked some good vacuums by mouth (practice with a gauge),
but your jaws will ache for a week...
On old refrigerator pump will draw a "very good" and fast vacuum. Every old
fridge has one... That is really the best way to do it for the common "no
money" solution. Say a prayer and toss salt over your left shoulder as you are
venting the FR-12 ;-)))
http://hot-streamer.com/temp/P5200028.jpg
Be sure to grab all the motor start caps and relays with the fridge
pump... Make a diagram of how it all hooks... Even few to many torr vacuums
produce very cool effects when mixed with high voltage!!
Pet store tubing, valves, and such are perfect with a little TLC. Cheers,
Terry.
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At least in my experience the refrigerator (or A/C) pumps tend to heat up pretty
fast. I have one running which will evacuate to a pressure where I can see
striations in a gas discharge (<1 mm?), but after a couple of minutes running it
gets too warm to touch. I've found that using a variac to drop the running
voltage down to about 30 (minimum
mine will run) helps the heating a lot but 5 minutes is still about it. Anyone
else having better results? Ed.
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Have a look at these articles:
http://www.belljar.net/refrig.htm
http://www.sas.org/E-Bulletin/2003-12-12/labNotesAS/body.html
Important points:
* These units need oil - If you're not careful, you can lose a lot when taking
it out of the original machine. You should rig an oil recovery system on the
discharge side. Cut tubes with a proper tube cutter, NOT a hacksaw. You
don't want copper filings in a close tolerance piece of machinery. Cheers,
M.
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Vac Pump From A/C Unit
Another, even easier, source for free vacuum pumps is dead window air conditioners. Most often, folks toss them because they developed a leak and lost their charge of freon. That takes care of the concerns about venting the stuff to the air. Dave.
Adam, Not much required to do the conversion -- just cut out the parts that you
don't need ;o)
Open the case, but do not cut any of the wiring. There are two sets of aluminum
foil fins -- the hot and cold side, with a fan or fans in between. You don't
need the fans or the fins. You can find the thermostat wires and jump them, or
use it as a convenient on/off switch. Tape up the removed motor leads to
prevent unwanted fireworks.
The compressor has two copper tubes -- an input and an output. Usually,
the vacuum input is the larger diameter tube, and the smaller is the output, but
it is easy enough to tell for sure after you have cut the tubes free and removed
the evaporator and condenser assemblies.
A small caveat -- the compressor runs submerged in oil, not unlike transformer
oil. I don't understand precisely how it's supposed to work, but some of the
oil gets into the compressor path, and your unit will "spit" oil droplets and a
fine mist of oil during operation, especially if you are moving large amounts of
gas through the system, as when you just
start to draw a vacuum. I'd suggest tying a piece of gauze around the output
end to control the mist, and bending the discharge tube downward into a can to
collect the oil drippings to avoid a slippery mess in your shop. Also, put
some sort of shutoff valve in the vacuum side of the pump, in case you lose or
shut off power while there is a vacuum in your test chamber. Otherwise, the
vacuum will fill your chamber with oil from the compressor. I don't know
or a way to get the oil back into the compressor, so eventually, the unit will
fail due to loss of lubrication. (In normal operation, it's a closed system,
so the oil is never lost or contaminated.) I believe that the cavity of the
motor housing is open to
the intake side of the system, so it might be possible just to pour the oil
(after you filter the dirt out of it) back into the inlet side of the pump, but
I've never tried this. Might be worth it to take apart a dead unit
just to find out, but I've never had time to try it.
HTH, Dave.
Original poster: "David Speck"
Eric, I worked for a summer a long time ago in a Singer air conditioner assembly
plant, though I didn't get to do much with the electrical end of things (mostly
tarring the roof, and a couple weeks doing inventory).
Each compressor motor is different -- no standard that I know of, and indeed, we
had many different models of compressors that were used, but each was wired
differently. Some were capacitor run motors, where there was an external
cap between two of the pins. Most of the models had a thermal switch
specifically designed for the particular compressor that cut out a start winding
after a second or two. Some of the big ones had three phase inputs, or a 4 pin
interface for fast and slow operation. I know that there was always a lot of
consternation when a new employee matched the wrong relay with a compressor.
If the compressor has a part number on it, you might be able to discover hookup
info off the web, or perhaps a friendly HVAC repair shop could look up the
pinout of the motor. See if there is a repair FAQ for Whirlpool systems.
Given the relatively broad availability of old A/C or basement dehumidifier
(same idea) units, it might just be easier to start from scratch with a unit
that is already wired up. Dave.
