Longevity of refrigeration compressor as a vacuum pump?

[DTJ]

Nice job even finding that data sheet to be honest. Not a 1st tier compressor manufacturer. Check out the top level domain for a laugh : www.transtech-co.jp. I did a quick comparo and something like a Secop TL5G is vaguely equivalent +/- enough not to worry about.

http://www.resluk.com/images/pdf/compressors/danfoss/tl5g.pdf

Capacity, displacement and dimensions are vaguely close. Certainly for this kind of thing. That takes 280ml of oil, so 100 will do the job, but keep an eye on the level. As long as you don't cook it, you should get many more than 40 hours out of it.

That's an odd looking page! You can count on the Japanese for being weird (at least from an Aussies POV anyway!)

Thanks for your help.

[DTJ]

Isn't it a bad thing to discharge R134A into the atmosphere?  Not wanting to do that sort of thing (with Freon or R134A etc.) certainly informed my decision (besides the quality & hassle factor) to get a proper pump and not ever try to salvage one.

It probably is a bad thing to vent the refrigerant gas to atmosphere, but given the vast numbers of fridges out there that either leak down or are scrapped and are mishandled on their way to recycling I don't think a few of us  de-gassing them to recycle the compressor is going to have an impact. (I'm from the days when we'd have fire extinguisher training courses and we'd all dump a couple of Halon extinguishers just for fun.)

I've seen hundreds of fridges stacked up at the local landfill / recycling place. I wonder if they bother degassing them there or if they just crush / bale and ship them back to china without bothering. Given the shitty attitude to recycling here in Australia I'm guessing its the latter.

[langwadt]

I'm impressed by the technical knowledge some of you have about using these kinds of pumps.
Long ago I played with surplus refrigeration compressors but ultimately decided to just pick up a two stage HVAC oriented rotary vane pump which is much more straightforware to maintain and run without worry and not have so much contamination concerns of spewing oil etc.

Isn't it a bad thing to discharge R134A into the atmosphere?  Not wanting to do that sort of thing (with Freon or R134A etc.) certainly informed my decision (besides the quality & hassle factor) to get a proper pump and not ever try to salvage one.
Wikipedia says:
https://en.wikipedia.org/wiki/R-134a

yes venting to the atmosphere is bad, but .. look at what is in the cans for air horns, air in a can  or non-flammable freeze spray

[DTJ]

I put about 80mL of very light oil in the compressor. It promptly spat a couple of mL out of the exhaust port after which just a little oil mist. The exhaust runs into a rag in a catch jar and there's now no visible exhaust.


So the PnP 'machine' is roughly finished. I need to add a pilot light to the compressor so I can see its on as it's too quiet to hear running. The clicking in the video is a couple of 12V solenoids for vacuum switching via a foot-switch in the box under the cylindrical vacuum reservoir.

The lighting is crap, the video out of focus and the phone camera wobbles around, the only redeeming feature it that it's not vertical video........   


https://youtu.be/jXjKYySPW0U

[amyk]

Nice job even finding that data sheet to be honest. Not a 1st tier compressor manufacturer. Check out the top level domain for a laugh : www.transtech-co.jp. I did a quick comparo and something like a Secop TL5G is vaguely equivalent +/- enough not to worry about.

http://www.resluk.com/images/pdf/compressors/danfoss/tl5g.pdf

Capacity, displacement and dimensions are vaguely close. Certainly for this kind of thing. That takes 280ml of oil, so 100 will do the job, but keep an eye on the level. As long as you don't cook it, you should get many more than 40 hours out of it.

That's an odd looking page! You can count on the Japanese for being weird (at least from an Aussies POV anyway!)

Thanks for your help.

That's not the actual manufacturer's page... this is:

http://www.tf-refrigeration.com/showproduct.asp?ItemID=72

As for venting R134A, indeed it is still used in "canned air" and such (although many have moved to R152A) ... but I suppose I would try to recover some of the gas, since it's still useful for other things.

[BradC]

As for venting R134A, indeed it is still used in "canned air" and such (although many have moved to R152A) ... but I suppose I would try to recover some of the gas, since it's still useful for other things.

It's pretty hard to recover in small quantities. Takes the best part of a hundred g or so to get through my recovery machine. The best way I've found to recover small quantities is to pack a small recovery cylinder in dry ice. Get it down below about -30C and it'll suck the last drop out of a system. Still, when a 300g can is $7 it's hard to justify the dry ice. A couple of fridgies I know (you know, the guys with the training and license) just purge it. Not a fan of the approach, but hey what do I know. I don't have the license.

[Siwastaja]

Since the compressor is running at way less than its design load, reducing the voltage by 20% or so using an autotransformer can let it run cooler.

It will have an induction motor which will attempt to turn at just below the mains frequency. Reducing the voltage and not the frequency will increase the current draw and it may struggle to start, causing it to overheat. It may work if you reduce the both the voltage and frequency to 20% but there's no guarantee it will work.

When the actual physical load (torque requirement) on the motor is smaller than expected (designed for), running at full voltage results in full current, reduced slip, and poor power factor. Reducing the voltage, i.e., to run in "field-weakened" mode, to get the operating point back to the optimum slip, which reduces the current and brings power factor back, is exactly the right thing to do in this case. This is exactly what VFDs do with their complex algorithms and math. But in principle, when less torque is needed -> reduce the V/f relationship, when more torque is needed -> increase the V/f relationship. (In so called V/f mode, V/f relationship is often kept constant, (what you suggest), which is unoptimal, but easy way out if there is no information about the system.)

Just don't go too far. You don't want to stall the motor, get near to the breakdown torque point, or be on the "left" side of the optimum slip; that's far worse than being a little bit on the "right" side (too little slip).

[james_s]

As for venting R134A, indeed it is still used in "canned air" and such (although many have moved to R152A) ... but I suppose I would try to recover some of the gas, since it's still useful for other things.

The way the law is in the USA, it's a federal crime to vent refrigerant into the atmosphere, so while you can legally vent R134A from canned air, once it has been put into a refrigeration system it is then classified as refrigerant and has to be recovered. R134A was developed as a non-ozone-depleting refrigerant but then it got classified as a greenhouse gas.

There are some other rather silly aspects of the law, for example if you extract the refrigerant from a system it is illegal to put it back in, you have to turn it in for recovery and charge the system with new refrigerant. The intent I believe is to prevent contaminated refrigerant from getting put into other systems and contaminating more of it but in practice it ends up being ridiculous. Fortunately the police are not likely to come arrest an individual but businesses do have to watch out for it.

The thing that annoys me is that along with banning R-12 they also banned R-22 which is another chlorinated refrigerant but it has only 10% the ozone depletion factor as R-12 and was widespread in domestic AC and heat pump systems. Propane is actually an almost perfect replacement for R-22 with slightly higher performance however it's illegal to charge a system with propane due to the flammability. R-410 is the "new" domestic AC refrigerant but it's not a direct sub for R-22, the equipment to use it has to be substantially physically larger and it runs pressures around double that of R-22 so you have to use heavier lines and brazed connections. With R-22 I could get away with silver soldering the joints and not need to flood with dry nitrogen. I wish they hadn't banned R-22, leaks are rare in domestic AC units, it was never used as an aerosol propellant or in leak-prone automotive AC systems the way R-12 was, and combined with the far lower ODP it really was not a threat in the same class as R-12. This is going rather off topic though.

[SeanB]

Will last a long time as a vacuum pump, though I would also go find a car fuel filter ( either the smallest plastic one you can get, or the standard VW fuel injection type) as an inline vacuum line filter. Keeps the dust down, and if you want to improve things get a standard compresser pressure switch and use it to turn off the compressor when you are at suction, and use in conjunction with an air reservoir ( old disposable 20lb/13kg refrigerant cylinder used as vacuum reservoir) so there is a suction reserve as well. Will need extra non return valve but worth it to have instant suction.

As to lifetime, they last a long time run this way, just keep a note of the oil level, and if it is too hot to keep your palm on the side of the compressor housing for 20 seconds it is time to stop and allow to cool down. they can generate quite a high head pressure as well, you can also use one to provide air ( though add the injection fuel filter as well to get more of the oil mist out of the air) to blow parts dry.

And as to refrigerant, I have enough R22 to last me, sitting still in the cans. As to wasting R134A, that stuff is expensive, not something you dump willy nilly, though of course with most modern fridge and freezers there is none any more, either R600 or something else, and there they will use POE oil even though mineral oil works with R600.

Oil is generally 32 viscosity, though some bigger ones use 68 viscosity oil, and I have a vacuum pump that uses the 68, so that is what I buy in 5l containers. Small vacuum pump uses it as well, and I change it regularly, and have seen many refrigerant guys with black sludge as compressor oil, seems like they have the original oil from new in there after decades of use, and never change it, just run it hot enough to boil the water out. I do the same just change the oil out regular, and when it turns the slightest bit milky or turbid. Oil is cheap, and I recycle it as well at a depot, though they just use the mixed and contaminated oil as either furnace feed oil or to blend bitumen.

[james_s]

Most refrigeration service vacuum pumps say to change the oil after each use, I've never done it that often though.

When I started working on automotive AC systems I used an old rotary compressor from a window AC unit as a vacuum pump to pull the air out of a system before charging. I set it in a bucket with a few inches of water to keep it cool. Worked pretty well although eventually it seized from moisture.

[johansen]

BTW what have any of you done to get down closer to UHV levels inexpensively for hobby purposes beyond the sub-Torr / xx millitorr levels that a 2-stage RV pump delivers?  Oil diffusion pump is one obvious possibility though still bulky / hard to come by.  I don't hear much about Ti-sublimation pump use for small scale uses or any possible alternatives along those lines maybe using Al sputtering or something vs Ti?  Turbo pumps would be nice but difficult / expensive / hard to come by by the time you get a good pump and controller and plumbing etc.

you need a good quality two stage rotary vane pump to pull a diffusion pump low enough to get it to work properly. but this is probably the cheapest route to go, unless you can get a turbo pump off of ebay working.

I have a duoseal two stage rotary vane pump (belt driven, about 500 rpm) and it can pull down to 10 microns with properly prepared 10w-30 synthetic engine oil when the oil is cold*. if i were to pay 100$ a liter for legit vacuum pump oil, it could pump down to 1 micron easily and this would be adequate for use with a diffusion pump. one micron is one millitorr. these pumps are relatively bullet proof and you do not need to buy the rebuild kits to fix them, you can make your own paper gaskets. this is almost identical to the unit i have. http://www.ebay.com/itm/Welch-Duo-Seal-Vacuum-Pump-/152488101537 --except this one is missing the air vent that lets you leak air into the second stage, so its possible that is a single stage unit, but its not possible to tell from the photograph, the second stage is inside the oil housing.

*by prepared i mean heating a gallon of it to 150F while pulling a vacuum on it with a harbor freight vacuum pump, for a few days.  diffusion pump oil is not cheap either, and you need a source of dry nitrogen to purge your vacuum systems because if you let air into it, you might cause the diffusion pump oil to ignite.

Anyhow, concerning a refrigeration compressor, i think its quite reasonable to drop the line voltage 20% to ensure that they can be used 24/7 without overheating. if it doesn't start it will trip the circuit breaker.

[james_s]

That Duoseal pump is almost identical to the one I have, which looked like it had been stored outside for a while but amazingly is able to pull down to something like 3 microns on fresh oil. Proper vacuum pump oil doesn't have to be that expensive, the stuff I have came from Duniway and I think was $25/gallon.  https://www.duniway.com/

[CatalinaWOW]

I can't add any to the expertise shown here, but can comment that an uncle of mine used a reclaimed refrigerator compressor as a vacuum pump for several decades.  I don't know how much he used it, but I am sure he did little if any maintenance on it.  Almost any reasonable duty cycle for these as a vacuum pump is absolutely benign compared to refrigerator duty.

[johansen]

They are designed to pump vapor only yes, but the compressor is cooled by a small amount of liquid refrigerant that returns to it, pours over the motor and vaporizes well before entering the intake of the compressor head. Too much liquid refrigerant returning to the compressor is bad because liquid does not compress. Too little liquid returning to the compressor is bad because the compressor overheats.

As a vacuum pump the compressor is doing almost no work, so assuming its line current is 40% of full load amps, then the copper losses which dominate the motor losses are only 16% of full load. this alone should keep the motor from overheating. however, the compressor coils and stator lamination stack can only radiate the heat away due to kT^4 radiation transfer for most configurations because there's no air in the compressor to convect the heat away. also, the few compressors i have dissembled, none of them would ensure any liquid would cool the motor windings or the stator of the compressor. if liquid returned to the compressor it will pool up at the bottom and boil off through heat transferred to the refrigerant by the cast iron piston assembly (work done on the gas heats it and the piston, the liquid refrigerant cools off the piston/cylinder assembly, so its sort of like a heat exchanger wrapped around the compressor). if you were to fill the entire compressor full of liquid refrigerant it would have to be about 70% full of liquid in order to get liquid into the piston, and it would have to be about half full of liquid refrigerant for the windings to be cooled by the liquid. The snorkel where the cylinder sucks in gas reaches up nearly to the top of the compressor and actually has a filter in some of them.. (i'm talking about household 50 pint per day refrigeration compressors and office water coolers, refrigerator compressors, nothing like a 1 ton scroll compressor which is completely different)

When used as a vacuum pump there is some conduction and convection heat transfer through the oil in the bottom of the compressor bowl, but i don't think that is significant because the heat transfer from the motor coils to the motor lamination stack to the cast iron block that makes up the whole assembly is rather limited. also, it would only cool the rotor, not the stator.

[johansen]

I don't think i was pulling water out of the oil when i degassed it, not initially anyway.  i had the oil in a 1 gallon wine jug and even if its cold, you pull a vacuum on it , you have to shut the pump off a moment later because it turns into foam instantly.


anyhow, legit vacuum pump oil is a much higher viscosity than 10w-30 motor oil. i don't recall if it was diffusion pump oil or Rotary vane oil, but i read a spec sheet on some commercially available stuff and it said the first 10% of it boils off at like  870F at atmospheric pressure. i was fairly impressed. no wonder you are supposed to be able to reach sub microns with a two stage rotary vane.


anyhow yes diffusion pump oil operates at its boiling point and the vapor pressure of the oil is what pushes it up through the jets, its cooled by the cylinder it impinges on and when you open it up to atmospheric air you've probably ruined it due to the water and or created an explosion hazard.

a  refridgeration compressor is no better than an aircompressor at pulling a vacuum. its can't do any better than the compression ratio its capable of, if its 20:1 you can't get any better than 1/20th of atmospheric pressure.

So those 2-stage RV pumps can pull ultimate vacuum doing your degassing for days of continuous operation without melting down in the garage, huh?

the ones from harbor freight, the vanes are nylon i think and if they absorb enough moisture to expand and get stuck the pump will jam up. the cast iron rotary vane pumps could corrode if you suck up enough contaminates, or the oil will just absorb all of it.

[johansen]

no, the harbor freight vacuum pumps are probably not worth buying.

i don't know to what tolerances they put the pump together but the two stage units are about 6 layers of metal. each layer bolts to the previous layer, and the last one has some screws that bolt to the first, clamping the stack together. setting reasonable tolerances like a few thousnaths of an inch, when you get to the last plate and tighten it down, the whole thing jams up.

[Trurl]

I've got a Samsung fridge compressor and an R410A refrigerant tank(check valve disabled/removed) both in mint condition - considering making a multipurpose vacuum pump with buffer tank.

The compressor likely has POE oil in it, and as it's been several weeks since I acquired it, it has been exposed(via the copper tubes' openings) to air, hence likely to have absorbed moisture and turned some of the POE oil back to acid & alcohol.

I'm considering the following procedure to replace the POE oil with a mineral vacuum pump oil :
1. Drain out the existing POE oil overnight.
2. Pour in about 100~200ml of ethanol* and swirl it around without turning the compressor ON(basically to flush out the remaining POE/acids/alcohols/moisture etc.).
3. Drain out the ethanol overnight.
4. Pour in about 150~200ml of mineral oil (BVA VAC235 vacuum pump oil) and operate the compressor for several minutes at a time(preventing overheating), multiple times to get the oil into the nooks and crannies.
5. Drain out the oil.
6. Repeat steps 4 & 5 another time, then fill again for future use.

*Regarding use of ethanol:
  Before pouring in the mineral oil, I'm considering pouring in ethanol(95%) and swirling it around as an acid absorber/flush solvent, based on info from US Patent 5,770,048 - "Method For Removal Of Acid From Compressor Oil"** which indicates that ethanol is able to absorb inorganic acid(e.g.HCl acid), separate it from the oil, vaporize, and eventually leave(evacuate from) the oil, sump, and compressor. It further suggests that if there is any organic acid, the ethanol would produce ester and a relatively insignificant amount of water(which would not be an issue as I'd drain out the ethanol+acid/ester+water remnants after the flush intended swirling).

** https://patents.google.com/patent/US5770048A/en
Note: The text in the patent mentioned above is repeated in a QwikProducts' knowledge base paper("Acids In Refrigeration")*** about QwikShot Refrigerant & Oil Treatment except the mention of ethanol is replaced with "QwikShot".
*** https://www.qwik.com/wp-content/uploads/2020/04/acids-in-refrigeration.pdf

Any thoughts/advice regarding the above would be most appreciated.
Thanks...

[NiHaoMike]

POE oil only becomes acidic if exposed to moisture and heated, I would just drain it out and refill with mineral oil.

[Trurl]

Ah~... Thanks for that useful pointer!
Good thing I haven't yet heated(torched) the copper tubing off the compressor yet. 
I had thought that carbon inside the unit resulting from any heating(to remove the copper tubing) could be cleaned by the POE inside the compressor, so I considered torching and removing the copper tubing before draining the POE, but I'll do any heating(torching) after draining/flushing the POE, as my primary concern is avoiding acid (which might eat away at the motor windings' enamel coating resulting in a short / motor burnout).
Cheers~

P.S.
Searched for "POE Oil Breakdown Temperature" and found an informative application bulletin entitled
“Compressor Overheating: Today’s Most Serious Field Problem”
https://www.parker.com/content/dam/Parker-com/Literature/Sporlan/Sporlan-pdf-files/Sporlan-pdf-010/10-207.pdf
in which the first half page mentions:

"Mineral oil will start to decompose at approximately 350ºF (400ºF for POE oil). As temperatures increase above this threshold, the oil starts to polymerize. In plain English this means that the molecules that constitute the oil’s makeup will start to combine into larger and larger molecules. First the oil is transformed into a dark thick oil, then a sludge, and finally a solid powder."