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Re: El Cheapo Vacuum Pumps

Original poster: Gomez Addams <gomezaddams@xxxxxxxxx>

On Aug 4, 2006, at 10:24 PM, Tesla list wrote:

Original poster: "Dave Halliday" <dh@xxxxxxxxxxxxxx>

Quick heads up -- this is a __venturi__ unit and needs a separate air
compressor to run.

If you download their service manual, you will see that it requires
4.2 CFM
at 90 PSI.

If you look at their air compressors, you will see that their item
with a 3Hp motor and a 152 pound shipping weight is only rated at
3.5CFM at

The vacuum pump is perfect for a large auto shop that already has a
high-capacity air system and wants to work on air conditioning
systems but
for anything else, there are better alternatives.

Your best bet for small vacuum pumps is to salvage the compressor
from a
busted refrigerator. Many times, these are tossed because the
breaks.  Some of them will have bad compressors but not all.

Refrigeration compressors don't "like" to work against a hard vacuum,
they are lubricated with an oil that isn't intended to have a low vapor
pressure, so if you're doing anything that needs to stay uncontaminated,
put a trap between your work and the pump.  I've heard of people getting
slightly higher ultimate vacuum from two refrigeration compressors in
series.  They pump REALLY SLOW however, so you need to be patient.  I've
always wondered about replacing the oil in one with proper vacuum oil
(mechanical pump oil) but have never heard of anyone who has tried it.

If you really need a decent vacuum, a proper vacuum pump will work
faster, and for longer than a refrigeration compressor.  Start hitting
industrial and university auctions in your area, or just haunt eBay.

I once found one at an electronics parts store they had taken in on
trade, I was able to pick it up for $50.  Often they leak, and often the
shaft seals just need to be replaced - kits to do this are usually
available from Duniway Stockroom and other places.

 - G.