Refrigerant recovery unit -- vacuum pump?

R12 is a refrigerant that is/was commonly used. It is gawd awful expensive these days. Small amounts can be recovered from refrigerator freezers and old working auto air conditioning units. But it will have contaminants in it, and the processing equipment to clean it up can be costly. Also, you will need a tester to identify the refrigerant you are working with to keep from mixing them, which makes them nearly worthless. The fractional distiller to separate mixes is very expensive. Also, you will need licensing and accreditation to legally be messing with this stuff. I know you need a license to buy it, but am not sure what you will need to sell it. Perhaps you will just keep it back for your own use. Not a bad idea if you have been to a car shop lately and priced AC work. Other common refrigerants are less expensive, but you would have to read the manual, or find out if you can do various refrigerants in YOUR apparatus.

HTH, and good luck.

Steve

Yes, you do need a license to buy the stuff, but that's a relatively moot point. You can get a certificate for about $20. There is an online test that you take to get the cert. I don't have the link off hand, but it's a pretty basic test. If you can't answer the questions, you shouldn't be messing with A/C anyways.

It isn't that big of deal to convert most R-12 systems to R-134. And R-134 is off the shelf. At least in Minnesota. Biggest thing is flushing the system of the old oil and using R134 compatible ester oil.

JW

"Steve B" wrote: (clip) you would have to read the manual, or find out if you can do various refrigerants in YOUR apparatus. ^^^^^^^^^^^^^ I got the impression from what the OP wrote that he wants to use this thing as a vacuum pump, not as a part of a refrigeration system. Lots of my friends use the pumps out of refrigerators and ice machines for pulling a vacuum--specifically, vacuum chucking on wood lathes. They work fine.

Yes, I am not really looking to get into the "refrigerant recovery" business. I was thinking about ripping out a vacuum pump from that unit and using it as a vacuum pump for general purposes.

i

Thanks Steve. What you wrote was very educational. I think that I would not want to go into refrigerant recovery, as such. I was just hoping that I could rip out a vacuum pump from that unit and use it for general purpose projects.

i

Depends on why you want a vacuum. Such a pump should pull at least

28" of Hg, which is useful for some purposes but not for others. It's fine for degassing molding materials, not nearly enough vacuum for sputtering mirrors or metallization.

What would you use it for?

My first use would be desoldering. I am not sure about future uses and whether I would need "deep vacuum". Good question though. In terms of percentage of air that such pumps remove, would you know how good are these refrigerant removal pumps?

Thank you

i

If it pulls 28 in of Hg, and atmospheric pressure is 29.9 in Hg.......do the math!

It would work fine for desoldering if you have a vacuum reservoir. The pumps are low volume pumps but a reservoir could provide a pulse of vacuum when you open a valve. A suitable valve might be the little pushbutton valve in a cheap blowgun, as:

I've seen these at HF for about $2.

A suitable vacuum reservoir might be an old 16.4 oz propane bottle.

A recovery unit has a lot of extra stuff in it because it has to cool the compressed refrigerant before it goes into the cylinder. You can probably strip out the pump but the other parts fall into that permanent junk box classification of "useless but to valuable to throw away". :-)

If it is in good condition the pump should pull down into the mili-torr range. My cheapo little RobinAir will easily peg a normal vacuum gauge. It can't keep up with my Sargent-Welch but then you can't pick up the S-W and haul it around the shop.

Thanks Don. I will see what kind of pump is in that unit, and will try to decide, but your information is very helpful. As far as "do the math" is concerned, you are right, but the answer depends on just exactly how much "above 28" the vacuum is.

i

Milli-torr is certainly very encouraging.

I think that if I cannot sell the unit for much more than a comparable pump is worth, I would just disassemble the unit and keep the pump.

Thanks Glenn.

i

I have a medical vacuum pump. Would it be suitable for A/C system evacuation? Any idea if medical pumps have to meet a lesser spec in terms of in/Hg?

I wonder if some people responding are confused with the type of "pump" you have. I do HVAC work and we have three or four recovery pumps around. None of them will pump much more than 10" of HG. We have several vacuum pumps to "vac" the system down when doing repairs that will do much lower vacuum, down in the 100-200 micron range. Recovery pumps are painfully slow at pulling a vacuum, their job is to remove refrigerant. Depending on what you plan on doing with it, it may be enough, or not! Greg

According to Rex B :

[ ... ]

I strongly doubt that. Medical vacuum pumps are used for removing fluids pooling in a area of surgery -- kind of like the pump put in your mouth at the dentist's. Medium flow, not particularly strong vacuum.

Strong vacuum would be likely to damage tissue if the tissue gets pulled against the intake.

Of course -- there could be other uses of vacuum in medical technology which could require high vacuums -- but I don't know what they might be.

I strongly suspect so.

The pumps used for A/C service are about the grade of the oil wetted pumps used as "fore-pumps" in high vacuum systems. They get the pressures down to a level where other technologies can take over -- turbo pumps, molecular sieve, oil-diffusion, and various others which can't even be *started* near atmospheric pressure. And those fore pumps need to run for quite a while to get even a fairly small vacuum chamber down to the pressure levels where the other technologies start out.

And the oil wetted pumps are really *too* good for something like desoldering. For that, I would suggest something like the Gast brand rotary graphite vane pumps. The oil wetted should be run for a long time after the majority of the air is pumped out -- in part to remove gases which have been taken up into the oil during the first part of the pumping. As they start, you hear a sound sequence like:

Glurk Glurk glurk Poketta Poketta poketta poketta ... tick tick tick "murmur" ....

with the "Glurk"s being large bubbles of air being passed through the oil bath, the "poketta"s being much smaller bubbles, the "tick"s even smaller bubbles, and the "murmur"s being the continuing motion with nothing measurable really being pumped.

The first few moments -- for however long the "Glurk"s continue, the exhaust side will carry some oil vapor with it. A lab pump usually has a trap on the exhaust to condense that oil and drip it back into the main pump. Sometimes, the exhaust is pumped to the outdoors, instead.

Enjoy, DoN.

For what you want it for, desoldering, and maybe some future vacuum clamping, it should work for you but with one, in my opinon hassle. Some vac pumps made specifically for pulling down A/C systems are piston driven and have a lubricant in their crankcase. Some, actually allow the Freon to go thru the crankcase not much unlike a two stroke engine. This is the case with your rotary automobile pumps and Refrigerator pumps.

What this might mean for you is oil mist in the exhaust side of your pump, and you need to catch it. If it is USED to lubricate the pump, you need to replace the lost oil somehow. Additionally, that oil mist is not beneficial in certain shops (like a body shop).

For what you want, and if this one does not work out, watch ebay for a Gast or Thomas oiless rotary vane pump like this:

These will run clean and relatively quiet, pull 26 to 28 inches, often plenty for clamping with a good seal. They can be put on a tank as long as you put a checkvalve in it so it does not run backwards when you shut it down.

Even though these are always rated as continuous duty, you can throw a swtich in line to cycle it on and off once the tank is full.

If your going to desolder, be sure to locate a tank or cleanable vessel between you or the pump... the solder has to go somewhere !

Grummy

Wonderful sound reproduction, Don! Some of my favorite sounds. Used to run a vacuum heat treating department in the 60's. Had forepumps that could get an 80+ cubic foot vessel down to 100 microns in a couple of minutes. We could fire up the diffusion pumps when we hit the switch for the forepump and the oil wouldn't get hot enough to backstream before we got in range.

Pete Stanaitis

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According to spaco :

Thanks. :-)

Now *that* is impressive!

Enjoy, DoN.