Longevity of refrigeration compressor as a vacuum pump? - Page 1
Forum section: electronics / projects

author: DTJ
author_rank: Super Contributor
timestamp: April 05, 2017, 05:47:25 am
content: Do we have any refrigeration techs here?I've got a compressor out of a small domestic refrigerator that I've re-purposed as a vacuum pump for my manual pick and place pen.See pics attached.I ran it for a while until most of the oil spluttered out the exhaust line. I've run it for a few hours and it still runs whisper quiet and pulls ~27"Hg vacuum.Any ideas on how long this will last running with just the residual oil inside the pump?

author: noidea
author_rank: Unknown
timestamp: April 05, 2017, 08:46:52 am
content: Hi DTJUnfortunately its a "how long is a piece of string question"Hermetic refrigeration compressors are designed with two things in mind, one they will always pump a small amount of oil out of their discharge as a refrigeration system is sealed and it circulates through the system and makes its way back to the compressor eventually, how much is still in the sump of yours is a mystery.Secondly they are also designed to be cooled by the flow of the refrigerant gas back over the windings of the motor inside the can, in most cases this is going to be below about 10 degrees C or if from a freezer below 0 deg C so running them with ambient air being drawn in puts them behind the 8 ball. Yours with the four pipes coming out of it indicates that it probably came out of a freezer as the extra ports are an oil cooler loop where the refrigerant gas passed through to further cool it further.The compressor label indicates it was designed for R134A refrigerant which would have probably been charged with POE Polyolester oil which is very hygroscopic and sucks up moisture which it then binds with and starts to form acid.All in all it is probably best treated as a disposable unit, some sort of separator / coalescer on discharge would help trap the oil that will continue to pump out of it which you could then pour back into the intake port periodically. Some way of filtering the intake would help and not running it too long will also help so it doesn't overheat

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 05, 2017, 08:54:07 am
content: http://www.randombytes.org/vacuum_pump.htmlhttp://www.belljar.net/refrig.htmhttp://www.belljar.net/fbleeconversion.pdf

author: Gyro
author_rank: Super Contributor
timestamp: April 05, 2017, 09:03:36 am
content: Maybe fitting a sealed screw type oil filler port in the top of the canister would be the answer (leaving the port open would probably seriously reduce the vacuum it could pull and increase the splutter rate). You'd have to fit a permanent oil collector on the outlet but you could then recycle the oil back into the compressor when it starts to run low. The act of pulling a vacuum ought to provide some degree of cooling.Hopefully you already have a non-return valve on the inlet pipe!Edit: Mechatrommer's links seem to have it covered.

author: BradC
author_rank: Super Contributor
timestamp: April 05, 2017, 09:12:19 am
content: Tip it up and pour the oil out of the suction line (that ties straight into the can). Measure how much came out.Grab the data sheet for the compressor and find out how much oil it holds. Fill it back up through the suction line with ISO100 air compressor oil.Do this periodically and it'll practically last forever, with the lifetime pretty much defined by how hot it gets. If you're not running it until its too hot to touch, and you're not sucking up noxious chemicals it'll pretty much last longer than you want it to. These compressors rely on refrigerant flow to move heat, and pulling a vacuum gives you very little flow, so in this application it's all about thermal inertia and convection around the can.Get the POE oil out of it ASAP.

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2017, 09:24:23 am
content: Quote from: BradC on April 05, 2017, 09:12:19 amThat seems like sensible advice. You may also have to flush it with several lots of compressor oil to get rid of the POE.

author: BradC
author_rank: Super Contributor
timestamp: April 05, 2017, 09:42:29 am
content: Quote from: Hero999 on April 05, 2017, 09:24:23 amI meant to say also as you are in Aus, grab 1L of cheap compressor oil from Supercheap or Repco. That'll pretty much last you forever.Yeah, a couple of flushes with mineral won't hurt to get the POE out, but to be honest just getting most of it out the first time will probably do the job. Tip it up so the suction port is at the bottom, and leave it to drain overnight. Do it when it's good and hot will make it go faster too.The process tube (the crimped and soldered one) is a second line into the can, so you can cut the end off that to let air back into the can to help you when you do oil changes. You'll just want to plug it up again for vacuum duty.A cheap and nasty oil separator for the discharge would be something like an aluminium can stuffed full of steel wool. Put the discharge pipe down the hole in the top almost to the bottom of the can, poke a couple of *small* holes in the very bottom to let the oil drain out and most of the vapor will get trapped on the wool on the way out, taking most of the oil out of the discharge . If you put the can over a container, you can measure the oil as it comes out and you'll know when and how much to put back in periodcially. Don't re-cycle it. Compressor oil is too cheap to stuff around with.

author: HighVoltage
author_rank: Super Contributor
timestamp: April 05, 2017, 10:09:07 am
content: One of the best oils for vacuum pumps is "Anderol-Oil type 555" and this oil works extremely well for this type of vacuum pump as well.I have done the procedure described above by BradC for changing the oil to the 555 and the pump is running for years already without any problems.

author: MagicSmoker
author_rank: Super Contributor
timestamp: April 05, 2017, 11:51:38 am
content: Personally, I'd ditch the refrigeration compressor and use an aquarium air bubbler pump instead.

author: CM800
author_rank: Frequent Contributor
timestamp: April 05, 2017, 01:52:53 pm
content: Could buy one of these maybe?http://www.ebay.co.uk/itm/220V-Vacuum-Pen-Suction-Pen-Smt-Smd-Repair-Air-Vacuum-Pump-Pick-And-Place-B-/381999483511?hash=item58f0f18a77:g:xw4AAOSwJ7RYThsl

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 05, 2017, 03:00:11 pm
content: Quote from: MagicSmoker on April 05, 2017, 11:51:38 amor this...http://www.ebay.com.my/itm/DC12V-Mini-Vacuum-Pump-Negative-Pressure-Suction-Pump120kpa-5L-min-With-Holder-/222259792486?hash=item33bfb74a66:g:mncAAOSwo4pYEEjui bought 2 of these in preparation for my next PnP project. easier to embed in 12-15V system, easier to control through mosfet switch, space saving etc. from my experience, the suction power of this (by putting finger on the suction tap) is much more than aquarium air bubbler (which i also have one laying about for years already). its just a bit noisier than the refrigerant compressor. and refrigerant compresor should last longer than this small oiless brushed motor.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 05, 2017, 03:03:00 pm
content: Quote from: MagicSmoker on April 05, 2017, 11:51:38 amNot even close in terms of how much of a vacuum can be pulled.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.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 05, 2017, 03:29:46 pm
content: if just there is an easier way to run mains line at 80%

author: MagicSmoker
author_rank: Super Contributor
timestamp: April 05, 2017, 04:23:23 pm
content: Quote from: NiHaoMike on April 05, 2017, 03:03:00 pmOkay, sure, but how much pressure differential and flow rate do you need to pick up a damn SMT part, anyway?I have a manual P-n-P system at my home lab for assembling prototypes (paid for itself many times over already) and it uses an aquarium pump for the vacuum pickup. It works perfectly fine, even picking up relatively heavy parts like 10mm aluminum electrolytic capacitors (need the rubber suction tip for that, of course).

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2017, 05:42:22 pm
content: Quote from: NiHaoMike on April 05, 2017, 03:03:00 pmIt 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.

author: CJay
author_rank: Super Contributor
timestamp: April 05, 2017, 05:44:25 pm
content: Yuo can buy parts designed for use with R134A aircon systems, particulate separators, filter driers, oil traps etc. Not terribly expensive but by the time you've bought them and plumbed them all in you're in the region of a decent second hand vacuum pump (a robinair, again an aircon service pump) so it's a value judgement as to which route to choose.Personally, if I had easy access to scrap/free refrigeration units and needed a vacuum pump that could pull that sort of level, I would most definitely give it a go.

author: james_s
author_rank: Super Contributor
timestamp: April 05, 2017, 05:51:58 pm
content: There is actually a line of commercially built super quiet air compressors that use refrigeration compressors. They are modified with a removable top on the hermetic dome and have a threaded dipstick to check the oil level. So long as you keep oil in the sump, a refrigeration compressor should last a good long time. They have a spiral groove in the shaft that pumps oil up from the sump and centrifugal force sprays it over the top of the compressor. One issue remaining though is that the compressors are normally designed to be cooled by a small amount of liquid refrigerant returning from the evaporator but with sensible duty cycles you can usually get away with running one open loop. YMMV but I used a refrigeration compressor as a small air compressor for years.

author: calexanian
author_rank: Super Contributor
timestamp: April 05, 2017, 06:52:48 pm
content: First thing. What are you doing with it? 27 inches of vacuum is not that much. Additionally without oil it will not last very long.

author: james_s
author_rank: Super Contributor
timestamp: April 05, 2017, 06:56:53 pm
content: Who said anything about running it without oil? Keep oil in the sump and they will stay lubricated. Might need to add a little now and then but it's pretty easy to rig up a primitive oil separator on the discharge line so most of the oil will condense and drip back down into the sump.

author: noidea
author_rank: Unknown
timestamp: April 06, 2017, 01:43:08 am
content: Quote from: james_s on April 05, 2017, 05:51:58 pmIt's not worth arguing on the internet but they are designed to pump vapour only. Liquid return to the compressor has its own set of issues.

author: DTJ
author_rank: Super Contributor
timestamp: April 06, 2017, 02:00:05 am
content: Wow, a flood of useful info guys.As perNoidea & Bradc, I drained the balance of the oil last night. It's clear and has very low viscosity. I only got ~1cc out of it.I've looked online at some compressor oil from local auto spares. I wonder if it will be too thick and I should just put some light machine oil into it?I'll try do do this slowly to avoid potential "hydraulic locking" thatnoideapicked up on.I had neglected to put a non-return check valve on between the compressor vac side and the rest of the gear -Gyro'scomment prompted me to run out and check to see if it had back flowed a pile of oil into the solenoids / reservoir tank. It hadn't. I had ordered a check valve with with some solenoids a few weeks back and fitted it.I'm going to put a catch can on the outlet with one of those stainless pot scourers in there to trap any oil mist.We have 6 monthly hard waste collections in our area so there is no shortage of fridge compressors - I'll see how long it lasts and if it does fail I can grab another one easily enough.The up side of these pumps is they are very very quiet (and free).As mentioned previously its for a manual pick and place set up. I'll post up some pictures of the final set up when it's done.Thanks for all the ideas guys.

author: BradC
author_rank: Super Contributor
timestamp: April 06, 2017, 02:20:59 am
content: Quote from: DTJ on April 06, 2017, 02:00:05 amI'll guarantee if you punch the model number into google and dig up the data sheet it'll take a *lot* more than 1cc of oil. More like 100cc.If you are worried about oil viscosity, use air-tool oil instead. It's ISO32 and much lighter than pretty much most refrigeration oils. You'll spew a lot more out though as the lighter oil will get whipped up into a thicker mist which will get ingested and ejected. Again, the manufacturers data sheet will tell you what oil it's supposed to take if you are really concerned. All of the reputable compressor manufacturers have comprehensive data on their devices.Don't worry about hydraulic locking. The suction tube empties into the shell, the actual intake for the compressor is right up the top of the shell. You could half fill the shell and not worry about a hydraulic lock. What you'd to do the rest of the mechanism with drag is another story altogether.noidea is right. These compressors are designed for vapor return. Having said that, a small amount of liquid return is generally survivable as it will evaporate inside the shell. It will generally result in oil foaming and cause lubrication issues though, so it's a big no-no in a functioning system.They are designed to cope with liquid, and if you read the compressor data sheet it'll give a maximum system charge. This is the volume of liquid refrigerant that it'll tolerate in the compressor shell at startup (designed for those one in a million instances when the compressor is the coldest part of the system and all the liquid migrates there). Usually in excess of a hundred g or so which for r134a works out somewhere around 80ml. That is less than the oil volume as the liquid refrigerant dissolves in the oil. When the compressor starts up the refrigerant starts to boil out vigourously and the oil pretty much fills the shell with foam. More liquid than specified can lead to damage through hydro-lock of the thick foam or bearing damage due to foam not lubricating properly. Always good to read the data sheet when building a refrigeration system

author: DTJ
author_rank: Super Contributor
timestamp: April 06, 2017, 02:48:25 am
content: Quote from: BradC on April 06, 2017, 02:20:59 amCheers Brad. I found a data sheet but it does not mention oil capacity. There's no doubt a more detailed data sheet somewhere.I've got some air tool oil. I'll try 100ml of that in it.http://www.transtech-co.jp/electronics/PWVK_ES_1.pdfIf I get 40 or more hours out of it I'll be happy.

author: BradC
author_rank: Super Contributor
timestamp: April 06, 2017, 05:04:06 am
content: Quote from: DTJ on April 06, 2017, 02:48:25 amNice 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.pdfCapacity, 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.

author: james_s
author_rank: Super Contributor
timestamp: April 06, 2017, 06:17:16 am
content: Quote from: noidea on April 06, 2017, 01:43:08 amThey 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. This is one reason the quantity of refrigerant in the system is somewhat critical, particularly in fixed orifice systems that lack a TXV to regulate the flow to the evaporator. The discharge line comes straight off the compressor outlet but the intake is inside the hermetic dome and to suck liquid into the compressor would require enough liquid returning to fill up the dome up to the level of the intake.While not my day job, I am licensed as a refrigeration technician and installed heat pumps and central AC systems on the side for a few years. There was significant discussion of this in the class I took to get certified.I probably should have been more clear though, I realize I've referred to "the compressor" both in cases where I'm referring to the whole assembly and in cases where I'm referring to the actual compressor inside the dome. Obviously you don't want to suck liquid into the compressor itself.

author: DTJ
author_rank: Super Contributor
timestamp: April 06, 2017, 06:47:42 am
content: Quote from: BradC on April 06, 2017, 05:04:06 amThat'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.

author: DTJ
author_rank: Super Contributor
timestamp: April 06, 2017, 06:57:35 am
content: Quote from: evb149 on April 06, 2017, 06:02:47 amIt 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.

author: langwadt
author_rank: Super Contributor
timestamp: April 06, 2017, 08:01:40 am
content: Quote from: evb149 on April 06, 2017, 06:02:47 amyes 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

author: DTJ
author_rank: Super Contributor
timestamp: April 06, 2017, 08:53:22 am
content: 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

author: amyk
author_rank: Super Contributor
timestamp: April 06, 2017, 11:56:56 am
content: Quote from: DTJ on April 06, 2017, 06:47:42 amThat's not the actual manufacturer's page... this is:http://www.tf-refrigeration.com/showproduct.asp?ItemID=72As 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.

author: BradC
author_rank: Super Contributor
timestamp: April 06, 2017, 02:09:05 pm
content: Quote from: amyk on April 06, 2017, 11:56:56 amIt'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.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 06, 2017, 04:33:35 pm
content: Quote from: Hero999 on April 05, 2017, 05:42:22 pmWhen 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).

author: james_s
author_rank: Super Contributor
timestamp: April 06, 2017, 07:02:01 pm
content: Quote from: amyk on April 06, 2017, 11:56:56 amThe 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.

author: SeanB
author_rank: Super Contributor
timestamp: April 06, 2017, 07:42:33 pm
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: April 06, 2017, 09:32:37 pm
content: 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.

author: johansen
author_rank: Super Contributor
timestamp: April 06, 2017, 11:36:40 pm
content: Quote from: evb149 on April 06, 2017, 06:02:47 amyou 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.

author: james_s
author_rank: Super Contributor
timestamp: April 07, 2017, 12:14:12 am
content: 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/

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 07, 2017, 12:17:14 am
content: 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.

author: johansen
author_rank: Super Contributor
timestamp: April 07, 2017, 02:24:40 am
content: Quote from: james_s on April 06, 2017, 06:17:16 amAs 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.

author: johansen
author_rank: Super Contributor
timestamp: April 07, 2017, 05:54:08 am
content: 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.Quotethe 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.

author: johansen
author_rank: Super Contributor
timestamp: April 07, 2017, 06:06:23 am
content: 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.

author: Trurl
author_rank: Regular Contributor
timestamp: November 10, 2024, 02:48:22 am
content: 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/enNote: 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.pdfAny thoughts/advice regarding the above would be most appreciated.Thanks...

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 10, 2024, 04:19:47 am
content: POE oil only becomes acidic if exposed to moisture and heated, I would just drain it out and refill with mineral oil.

author: Trurl
author_rank: Regular Contributor
timestamp: November 10, 2024, 04:38:39 am
content: 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.pdfin which the first half page mentions:"Mineral oil willstart to decompose atapproximately 350ºF (400ºF for POEoil). 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."