Making a vacuum pump from a compressor

Re: Making a vacuum pump from a compressor

Bill Howatt

>Bigger is better.

Be extremely careful as it can be hazardous to your health - make sure you keep it upright as the oil can run out onto the floor and your wife will .... DAMHIKT.

You just need the compressor and the electricals to make it go. You might want to keep an eye on it when you run it at first to make sure it doesn't get too hot and shut-down on you. I have heard of people blowing air on them with a small fan if necessary. This might be a balance between the loss of cooling from the circulating gas and less work being done by the compressor when acting as a vacuum pump (I think it is less).

I used one from a dehumidifier and it pulled around 26". Where you lose is in the pumping speed and thus leak tolerance unless it is a large unit.

Bill

Bit more

Bill Howatt

>You should put a filter on the inlet side so you don't suck a bunch of dust into it. I have a car fuel-filter and a coarse filter made by stuffing some filter material into a clear plastic tube ahead of it. Surprising how much dust gets caught in the coarse filter over time.

You should have a valve to bleed air into the system to reduce the vacuum if necessary. If using on a lathe you can break a large thin bowl with excessive vacuum.

Get a gauge, they can be found for less than $10, without it you are flying blind.

Bill

Please do not do this....

Jesper, Denmark

>The refigeration loop is a closed system containing both oil for lubricating the compressor and a CFC, usually Freon 12, which is a greenhouse gas. This has to be recovered and destroyed to avoid the gas getting into the atmosphere, where it basically will stay forever.

Letting this gas out is illegal. It must be handled by a licensed recycler.

Also, the lubrication of the compressor relies on the closed system, where the very small amount of oil stays in the circuit.

The CFC (Chlorofluorocarbon) is not hazardous to you personally and it is not flammable, but will escape if you open the circuit. It is only illegal and environmentally irresponsible to do this.

Re: Please do not do this....

Gary Evans Tallassee, TN

>Hi Jesper,

Not to worry, I plan to have the freon professionally removed, if the unit I choose is still charged. It may well be that some of these boxes will have a good compressor but no gas. That would be my first choice.

As far as lubrication, my understanding is that the stationary compressors which are used in these appliances have their own lubrication supply. See Bill's comment above about turning the compressor over. You are correct that automotive systems carry the lubrication with the gas.

Gary

Re: Making a vacuum pump from a compressor

Mike Jurnigan in Suffolk

>Back in my High School days, I built a Particle Accelerator (Atom Smasher) as a High School Science Project. It had a pretty elaborate vacuum system on it. Being a high school student with a limited budget (working for fast food joint at $1.10 hour) the plans called for using non-scientific supply house materials. The vacuum pumps were compressors hooked up backwards. One vacuum pump was a refrigerator compressor that was modified. The biggest thing that had to be done was wire the electricals up with a momentary switch in the start circuit. You had to flip the switch on and then press the momentary switch for it to start. If I remember correctly the compressor case had three terminals on the side and you had to run the hot and neutral to the outer terminals and the momentary switch was jumpered between the hot and the center terminal. The only problem I had with this arrangement the first compressor had an internal short in it and I found out the hard way about the short. (I still don�t like being shocked after that incident) The other vacuum pump was a walk-in box compressor. It was made up just like an air compressor with a separate belt driven motor. No major modifications there. If you have any questions just ping me.

Mike

Re: Just Fine

Mark Mandell - Gone Round In Jersey

>I use two compressors from dehumidifiers pulling for my vacuum system for my Stubby lathe. Mine have been working just fine for 4 years now, and pull about 28" of vacuum. Do note, however, that you must have a small fan blowing on the compressor housing(s) during use because these compressors have internal thermal overload disconnects that will trip and shut them down after not many minutes unless cooling air is used. In A/C or dehumidifier units, the heat exchanger/circulation fan does the job. If they get hot and stop, you get to follow the bouncing bowl in your shop. DAMHIKT In my rig, I actually reused the circulating fan from one of the dehum units. The pic shows how the compressors are set up. They have since been enclosed in a box with the fan drawing cooling air through a small furnace filter at the opposite end to keep things clean inside. Whole thing runs nice and quiet. Note that a refrigerator compressor might work for say a veneer press, but you'll need a much bigger unit for a lathe because these closed loop compressors pull rather low CFM. That's why I use 2, taken from 50-pint dehumidifiers or at least a 2+ "ton" window A/C unit, so that I've got almost 5 CFM in draw to compensate for wood porosity.

I get the compressors for FREE from an appliance shop who's glad to give me their junk after the freon has been removed. I therefore have several "spare" compressors on the shelf in case one in my set-up fails.

As stated, you MUST put a good suction filter between these compressors and your appliance. Dust will kill them very quickly as it will gel the lubrication oil. Lastly, I exhaust them into a condensing coil with a drip cup to recover any oil mist. I also give them a "drink" of a tablespoon of compressor oil after every 2-3 hours of use.

Hope this helps

Re: Making a vacuum pump from a compressor

Larry Clinton At Frankfort (Central)., Indiana

>As others have said - it will work fine. I would follow the advice above to obtain the largest possible, and use a belt drive unit if possible. Then you have the option of changing pulleys to match up motors hp / speed. I'm not sure about the type units you have, but many of the household refrigerators now are using a "scroll" type compressor. Not sure if the lube for these units are similar to a car or the older piston type units. I had a belt drive piston style unit from a walk - in refrigeration system that I used for a compressor for several years. The motor finally gave out, by then I had my 60 gal shop compressor so I tossed it. I have a PIAB vacuum system that was tossed at work I intend to use for my vacuum system. These are air venturi style units that worked well. I also have a vane type pump I purchased at an auction, but when I got it home I found it was froze up. I may repair it. Might wish I had kept the old piston unit fore its thru.

This should go into the Articles & Reviews section

Ken Grunke from SW WI

>I looked there and couldn't find anything on refrigeration vacuum pump adaptions. I hope Ellis can add this. Thanks Mark!

Re: Making a vacuum pump from a compressor

Bill Turpin in WNC mountains

>Gary, do everything above. Refrigeration compressors do not have piston rings. Ref oil dissolves freon and freon dissolves ref oil. Just like H2O/alcohol, the mixture can be 0% to 99%. You can not separate them mechanically, so the comp. manufacturers do not try. Sooner or later the crankcase will run dry, because of non-returning freon/oil. There is not a separate oil loop. Some small comps have a cooling loop for the oil, but it is not separated from the freon. Fractional comps can have several qts of oil. Add oil as mentioned above. Ref oil is special and about $45/gallon. Have an exhaust filter box that will indicate how much you are loosing. Most ref comps are refrigerant cooled along with condenser fan cooling. ADD MORE AIR COOLING. Dehumidifier comps probably require less ref cooling than others. Freezers are the worst. Be sure you get the capacitor/s and the start relay. This relay drops out the start winding after motor gets to about 2/3 running speed. ( half second)

Piping: Vacuum flow is inversely proportional to the square of the orifice or distance. Hillbilly translation, half the orifice, one fourth the flow. Twice the distance, one half the flow. Figure this on cross-sectional area. A 3/8 hose will pass 4.95 times as much as a 1/4 hose. Good luck!

Bill in WNC mountains

NC Refrigeration License # 2821

Re: Oiling the pump.

Larry Clinton At Frankfort (Central)., Indiana

>Bill, as an Engineer for over 39 years, I would not hesitate to use a good grade of automotive motor oil to squirt in the intake every hour or two of use. The refrigeration oil is needed when the unit is used with freon and as a cooling system. I doubt there would be any problems using a standard lube when using it as a vacuum pump. I know there isn't any with piston pumps as I used motor oil in mine for several years. I don't think there is any material in the compressors that would be harmed by motor oil - it is probably a better friction inhibitor and darn sure cheaper and easier to obtain.

Re: Oiling the pump.

Bill Howatt

>I guess I split the difference. I put air-compressor oil in my old 2-cylinder piston refrigeration pump. It has a separate motor and apparently was used on a farm 50 years ago to cool a large water tank that the cans of fresh, warm milk were put into to cool quickly.

Bill

Re: Oiling the pump.

Bill Turpin in WNC mountains

>Vacuum pump oil and (I assume ref oil) have a low vapor pressure. At low pressure/high vacuum, the vapor pressure of standard oils will compete with the ability to reach more vacuum. Since my turning experience has not incorporated vacuum chucking yet, I do not know whether this is a factor or not. I was just trying to give Gary as much info as possible.

Since use of belt drive compressors was mentioned, I will throw out some more. Standard ref oil has a viscosity of 150, belt drive is 300. I do not know how this relates to lube oil weight ratings.

Bill in WNC mountains

Re: Oil Choice

Mark Mandell - Gone Round In Jersey

>I use synthetic "Select" compressor oil as it does not carbonize in the compressor like motor oil will do. This at the rec of both the appliance guy and the tech who serviced my shop compressor (Ingersol-Rand).

I only add enough to make up what gets condensed in my little exhaust cup collector. With four year's use out of otherwise "junk" compressors, all while pulling against better than 20" of Hg., I think I've gotten good advice.

mm

Au Contraire, Ken *LINK*

Garrett in Victoria BC

>There is an article there per the link below, but I acknowledge that this thread adds quite a bit of useful info and I will incorporate it.

Cheers, Garrett

Editor, Articles & Reviews


Vacuum Pump

Re: Oiling the pump.

Bill Howatt

>I don't think vapor-pressure is a factor this type of application since the vacuum is nowhere near what is commonly called high-vacuum work where pressures of a millionth of a Torr (1 mm of Hg) and less are the norm. These compressors get a best vacuum around 28" of Hg compared to the theoretical maximum of 29.9" and maybe that is partially due to vapor pressure issues.

Although it depends on the area of the workpiece under vacuum, 15"Hg or more vacuum is usually sufficient to hold most pieces very well. It is not unusual to lose several inches of vacuum due to stray leakage and workpiece porosity which totally swamps any vapor pressure issues.

Bill

Re: Making a vacuum pump from a compressor

Larry Marker in Alabama

>Jim Halbert, who used to hang out in Badger Pond, wrote up a good article on how to do this. I have a copy of his write-up. I don't feel that I should upload it here without his permission, but I'm sure he wouldn't mind me emailing it to anyone who wants it.

If you want a copy, send me an email and I will send it on.

Larry

Vacuum pump and chucking reference *LINK*

Bill Howatt

>The link to the pdf below gives more info on the different pumps, vacuum chucking methods than you probably care to know.

Bill


Vacuum pumps and chucking

Thanks so much...

Gary Evans Tallassee, TN

>for all the good information.

I think I have enough now to not only create a vacuum pump, but also keep it alive for the forseeable future in my new woodturning shop.

Thanks,

Gary

Re: Thanks so much...

Sarge

>Hi, looks like you have gotten some good information on making a Vac pump. It can be done and will work using a compressor but as mentioned oil return is important. Depending on which type of compressor is used refrigerate type etc makes a difference. Do not exxpect this compressor to pull a real good vac for very long. Its cheaper to just purchase a true vac pump. Reason is a compressor from a a/c typically is refrigerant cooled , yes they have water cooled compressors also, thus you will be indesting ambient air this will over heat the compressor in time with no oil return it will break. A piston recep compressor will over heat and damage the valves thus making it useless. For a few hundred dollars you can find a real vac pump and just keep the oil changed it will last for years. I have been doing this longer than i care to admit, advise is free. Happy wood working guys. Great site... 82nd Airborne, all the way"