where should I go to get cheap fridge or AC compressors? i need two compressors to pull a low vacuum, like a couple torr or so. people talk about getting scrap window units or old broken fridges for really cheap, but is that actually a thing still? like would a local appliance repair shop just have some busted compressors they'd sell me for pocket change?
>would a local appliance repair shop
I don't think those exist anymore. Put up an ad. Go to your local dump and check if they have a hazardous waste day sometimes once a month or once a quarter where people can drop off fridges and air conditioners.
you use vacuum pumps to pull vacuum, compressors are made for compression and will suck at sucking.
they can pull some vacuum but nowhere near what you need.
you know a vacuum pump operates on the same principal.. but a vacuum pump usually has 2 pistons to obtain a better vacuum and is a 2 stage process whereas a ac compressor isnt because it doesnt need to pull such a tight vacuum but only compress the refrigerant gas.
maybe you can help me. all the automotive vacuum gauges only go up to 30 inches of mercury. I need one to go to 40 because I'm tuning my ford a bit.
why dont you google it. have a nice day.
>you know....
well yes i do know thats why i try to teach you. compressors have pistons and vacuum pumps have vanes, compressors have a compression ratio of whaterver-1 and vane pumps gazillion-1, they are basicly zero clearance. its in their very nature and you cant really fix this.
to make vacuum you need to first create a vacuum inside the pump or compressor lower than the pressure in the container being vacuumed, thats how you suck out the air. then you need to compress that air so much you can actually push it out into the atmosphere. if you dont have that compression ratio nothing happends sinse your cylinder or vane will at the sucking motion return to the same pressure as last time it was there.
when in a damn hurry i have vacuumed pretty large commercial refrigeration system by using the actual refrigeration compressor, it will draw a vacuum down to about 0,3bar absolute pressure within minutes, much faster than any vacuum pump. thats still not close to vacuum by our standards and i need to run the vacuum pump to pull it all the way down i just saved a few hours pulling out 2/3 of the air.
Nice blog homosexual. Perhaps you should learn to spell and use proper grammar.
thanks for the details anon
it's good you gave your contextqully fittong practical use case to further make things undrstandabble for a dabler like me
is it usually a tradeoff of high volume throughput vs high differential pressure?
i guess piston pumps can both compress and suck to more similar capacity?
here's a guy getting 60 torr on a reciprocating fridge compressor.
this may be fine for something like vacuum distillations.
this shouldn't come as a surprise, it's a similar operation to a diaphragm pump, which also is used for low vacuums in chemistry applications. the difference in the two is that a diaphragm pump has a plastic seal in front of the piston.
window units often have a rotary compressor. newer ones may have a scroll compressor. this should be capable of a few torr. not to the levels of a roughing pump, but that's not what he's asking for, he's asking for a couple torr. a window unit compressor would work and is probably cheap.
here's the type in the OP, a rotary compressor.
?t=209
this is a scroll compressor, also from an AC unit.
?t=725
i'm not going to meme on you, but a compressor and a vaccuum pump are fundamentally the same machine. you compress in front and vacuum behind, necessarily. a fridge compressor cannot compete with a turbomolecular pump in the same way that a lawnmower cannot compete with a F1 car.
absolutely, 100%, if you cut a compressor out of a window unit and hook it up to a gauge, that fricker will draw down to a a few torr. if that's all you need, i cannot think of a cheaper way to do it. i would figure that calling some AC repair places, maybe checking a junkyard, or just checking craigslist, you could probably get one for nearly nothing or maybe free. they are often fine even when the unit is "broken".
or, cough up 60$ and buy a vacuum pump from the harbor freight and get down to sub torr. you can abuse the frick out of them and just change the oil and they're good to go.
Cool, made me look up the different types.
Liquid ring pumps are cool too (but offtopic of course)
I have one in my garage if you need one. Where you at? It's in an old dehumidifier and still works great