Re: Vacuum Pumps

Can a reversed compressor from a household fridge be used for a vacuum chuck? Probably not, same as lamp dimmers for VS, but I'll ask. Arch

Fortiter,

I think that the answer is yes but there are two problems.

First you have the problem of disposing of the coolant legally -- you are not really supposed to vent it into the atmosphere.

The second is lubrication. These closed freon-based systems mix a lubricant in with the freon to keep the system running. Since you are converting it to an open system you must find a way to keep it lubricated and a way to keep the lubricant from spraying from the output side and onto everything in your shop.

You will find several articles around about using an auto air conditioning pump in the same way. The old York compressors are a favorite and available at any junk yard.

Bill

Yes they can. I used one from a junked dehumidifier and the oil stays in the bottom just fine. It would pull about 27" of mercury but the only problem is they don't have a real high pumping capacity so if you have "leaky" wood it can be a problem. It is surprising how little vacuum it takes to hold a piece 6" in diameter or more. You should also make sure the pump doesn't get too hot and trip out or stop working. A small fan placed near it helps a lot. You want to get as large a unit as possible so a room air-conditioner or dehumidifier are probably better than a fridge unit. I don't know how you tell if the unit is a circulate-the-oil-with-the-freon type (scroll??) or a reciprocating piston type. Older ones are probably piston.

I was since given a much larger compressor from a very old farm milk cooling system. Has a separate motor and looks more like a paint sprayer compressor. I fixed it up and now use it instead of the dehumidifier compressor because it has more pumping capacity.

Billh

the short answer is no - due to inadequate flow - maybe from a humongous commercial unit, but not from your home refrig. But, those old compressors are useful for drawing a vacuum on your automotive AC when you work on it (or other uses where significant flow is not an issue)

there is also the point that they require lubrication, typically by pumping some oil through the system, so it's best to squirt a little oil into their intake every once in a while.

"william_b_noble" wrote: the short answer is no - due to inadequate flow - maybe from a humongous commercial unit, but not from your home refrig (clip) ^^^^^^^^^^^ The short answer "no," is slightly too short. One of these compressors was demonstrated at a meeting of Westbay Woodturners a few months back, and it worked fine. It is true that the low volume makes it vulnerable to small leaks, and, for that reason I would not want it. On the other hand, it ran so quietly that you could hardly hear it. A friend, and member of Bay Area Woodturners is in the ice machine rental business, and he junks quite a few units that still have good compressors. These are larger than home refrigeration units, and they work REALLY well. Club members are lined up waiting for them.

The lack of lubrication has been mentioned as a problem when they are used this way, but, so far, no one has reported any trouble. We think the light loading in vacuum service, along with the fact that turners don't run them in continuous service for years on end, means they will serve OK.

I am new to this thread, and was wondering if there is an online article, FAQ or WEB page detailing the process of using this type of compressor either as an airbrush compressor or as a vacuum pump.

An ancient, but working, 220v wall airconditioner unit was taken out of service and I have an opportunity to obtain the compressor for free.

Thanks.

Tim

This site might help?

- Andrew

And, by the way, can a vacuum pump's outlet be used to pump up an air tank? With the proper fittings of course. I have a Gast 1/4hp 4.5cfm unit and would occasionally like to pump air into a small (5 gal) tank with it to around 75psi.

- Andrew

Thanks. That was exactly what I needed to get started.

Tim

AHilt> This site might help?

My thanks too, Andrew, and for all your good advice. Arch

Fortiter,

1. you can find my article on vacuum pumps in the tips section of
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1. you can use some vacuum pumps for compressors. The vane type pumps are fine, most will deliver around 35 psi. Piston pumps are a different matter - they must have an overpressure relief valve, or you need a pressure switch to stop them when there is adequate pressure. If your gast pump is the vane type, or the wobble piston type, you won't get 75 psi. Ratings for the pumps, both pressure and vacuum are on the gast web site
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   if I remember right). If you don't have a shut off switch or relief valve, you will stall the pump when you stop blowing air and burn out the motor.

The pumps I sell sometimes have these relief valves and sometimes don't - you can buy the valves of course, you will want to know what the stalling pressure of your pump is and then choose a valve that is several PSI below that. Vane type pumps will be ok though, they don't stall, instead they just free run when the outlet is blocked.

Thanks. It's a rotary vane 0523. It doesn't have a setup for pressure but that's not a problem to add. Still, I don't see that it's going to be worth it for what I'm wanting to do on the compression side of things. I'll just tear down an old compressor and use that.

I used your and others notes on making a rotary union. Works quite well and was a heck of a lot cheaper than the Oneway.

- Andrew

There is no reason you could not use the refrigeration compressor to provide pressurized air to a tank. The biggest concern is to ensure that the compressor does not loose all of the oil.

During a normal refrigeration cycle, it is entirely feasible for the outlet side of the compressor to exceed 100 PSI.

Dave

AHilt> And, by the way, can a vacuum pump's outlet be used to pump up an air tank?

Thanks for that information Dave. Unfortunately, I don't have and wasn't talking about a refrigeration compressor but I'll keep that in mind in case I ever do. The specs on the Gast vac pump that I do have shows that it's only rated up to around 30 psi compression.

- Andrew

A little engineering info on this subject. Refrigeration oil will dissolve freon, freon will dissolve oil. They can not be separated in the discharge from the compressor. Therefore no attempt is made to separate them. Most ref compressors do not have piston rings. Most ref compressors are cooled by the relative cool suction gas returning to the compressor. They are also cooled by additional air blown over the comp body.

Vacuum pumps use vacuum oil which has a lower vapor pressure than regular lubricating oil. This vapor press adds to the low side pressure of the system and yields a higher low side pressure(less vacuum).

If at all possible use a cooling fan to keep comp cooler. A fan can usually be scrapped from the same unit as the compressor. A freezer compressor is designed to pump a lower pressure(more vacuum) than a cooler compressor. Within these guidelines most of this thread is accurate. Refrigeration oil is quite expensive, much cheaper vacuum pump oil could probably be substituted. I have not tried this.

Bill in WNC mountains NC Refrigeration License #2821