Vacuum Chamber Casting Unit (was: a Big Sucker)

Vacuum Pumps

Here is a thread I saved from newsgroup about a year
ago, plenty of interesting stuff. Also, I remember another article (which
I can’t locate at the moment) discussing the use of a simple laboratory
water-aspirator to evacuate an empty barbecue gas bottle as a ‘store’ for
the vacuum. The aspirator gadgets attach to a household water tap of
sufficient pressure, and running the tap for ~10 mins is enough to
evacuate the average sized bottle. The gas bottle was then used for 5 or
so vacuum-assisted castings, or to vacuum-invest.


Cut the pump out of a junk refrigerator or a/c. These sealed compressors do
make very good vacuum pumps…as long as they have mineral oil in them.
They rely on the oil, not just for sealing, but to stay alive. One must use
a water vapor trap and filter on the inlet, as the pumps are designed for
a very clean and dry internal environment. Of course, since the things are
FREE at any landfill, it doesn’t matter how long they last, I suppose. Some
of them will deliver a vacuum in the order of 10 ^-3 Torr.

The compressor from an air conditioning or refrig. can be used. It is self
contained and the same units sell for $300+ in the catalogs. Just be
careful when you remove it. There is oil in the system, but for the price
you can live with it.

You can also use it to feed air to a propane/air torch, mine works great!

First - <<< BE CAREFUL - I have done this but - PROCEED AT YOUR RISK I use
a compressor from a small ( window size ) air conditioner. First you have
to make sure the unit does work. It does not have to cool, just run. The
unit is full of oil and refrigerant. This must be released. Cut the line,
and stay out of the way! The gas is UNDER PRESSURE!!! After the gas is
released, finish cuting through the lines, (two per unit) and carefully
remove the compressor from the unit. Be carefull of the electric lines!
Carefully work the wires loose and you have the start of your vacuum

To wire it up, you must use the capacitor (the silver metel can, maybe 3
in. long, 1 in thick, 2 in wide) that came out with the wires when you
removed the unit. CAUTION these things hold an electric charge and
can hurt real bad!!! With an insulated screw driver, touch the tabs on top
of the capacitor together, this should made it safe. Three wires come out
of the compressor, white, black, and red. Connect the white wire coming
out of the compressor to the white lead of the power cord. The black lead
from the compressor and the black lead of the power cord both go to ONE
terminal of the capicator. The red lead from the compressor goes to the
other terminal of the capicator. This is needed for the motor to start
properly. All this stuff needs to be insulated and made safe!

To use the pump, find compression fittings (at the hardware store) that
fit the tubes on your unit. Watch the oil. If I’m correct, these are
rotary pumps and need the oil to live for long. A few drops of minerial
oil in the air intake every so often will help a lot. I use a 12 in. square
piece of 1/2 in. LEXAN for a base. LEXAN will not shatter. Get it tapped
(threaded) to take a screw in fitting that will allow you to connect to
your pump. My plastic cost $12.87. I found some 1/8 in. red rubber gasket
material at the local contractors yard ( they use it for pump gaskets)
cost $3.00, makes a good seal between the bell jar and the base. Bell jars
are about $45.

Hope this helps. Let me know if you need more info.

Have a good day :slight_smile:


1 Try to find an fridge that was junked for any thing but compressor
failure (for obvious reasons)

2 If at all possible, get someone to remove and reclaim any freon left in
the system before you cut into the tubing. The stuff’s not very good to
release to the atmosphere, and is illegal to release in the USA.

3 There will be two tubes, one normally larger than the other. The large
tube is suction the smaller is outlet. On a working unit, the suction is
the side discernably colder than the other.

4 If you are only going to use the suction side, attach your connectors
with either solder or compression fittings (the ones sold for gas work
well). On the outlet side, attach a short section of pipe that expands at
least twice the size of the tube then reduces again. This is to trap some
of the oil that will come out of the compressor. To the reduced end of the
trap add some kind of filter.

5 Avoid letting the unit run dry of oil (unless you’ve a plentiful supply
of deceased fridges). Simply add a bit through the suction periodically.

6 Avoid running it too long without attendance or a break. If it’s too
hot to touch, let it cool off. Normally the refrigerant helps cool the
motor, and air isn’t as effective at heat transfer.

6 The best way to use the outlet side for compressed air, is to use it to
pressurize a tank, and use a filter/dryer on the outlet of the tank. Such
tanks can be had at places like wal-mart for under $30.

Most of the necessary fittings are standard hardware store items. The
filters and dryers are available at a welder’s supply (much cheaper,
usually, than jeweler’s supply).

Hope that this helps some.

Remember, though, deliberate releasing Freon to the atmosphere, really is
against the law. The odds of getting caught may be low, but the fines are
really steep.

Ron Charlotte – Gainesville, FL

Laurence Veska.