General > General Technical Chat
Modified compressor.
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BradC:

--- Quote from: amyk on March 29, 2021, 02:15:16 am ---Maybe there's something about these relatively newer (more "environmentally friendly"? ::)) systems that causes them to fail more often --- they could be giving them barely enough oil to begin with, a carefully calculated amount that ensures the bearings will wear out.
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The older systems all used mineral oil and an incredibly stable refrigerant. It was pretty bulletproof *and* they were built to last. They were really tolerant of sloppy manufacturing / assembly practices.

The move to HFC refrigerants and synthetic oils results in a system that is far less tolerant of contamination. Pretty much every failure I've seen over the last 10 years has been leak related. Cheaper materials in the evaporator or pipework results in a small leak which eventually results in a bit of moisture being pulled into the system. On the old systems, a good vac and replace the drier and it was all good. With the newer refrigerants and oils a bit of moisture starts to hydrolyze the oil and refrigerant leading to acid, and the rot starts from there.

I've seen a swathe recently of aluminium pipework buried in foam where something in there has caused mass corrosion of the aluminum leading to catastrophic leaks. For all intents and purposes it looks like the blowing agent used for the foam has formed acid over time. They're just built down to a price these days. I don't recall ever seeing a compressor failure that was wear related. My neighbours split seized a compressor, but on teardown it was a bit of manufacturing leftover (looked like either swarf or solder) that rattled around for 15 years until it lodged in the compressor and jammed it.

The move to a hydrocarbon refrigerant should help with acid long term, but it still depends on the oil used and how cheap they can engineer the remainder of the system.
Berni:
Leave the oil as is, these things don't need oil changes.

We got a DIY altitude simulation chamber that uses a refrigeration compressor to pump it up and down. Has been running for many years just fine. Just stick filters on the ports to keep dust out and have a oil separator close to the output so that the captured oil can flow right back down into the compressor.

Corrosion is however a problem due to moisture. You cant grantee dried air when you are using it as an air compressor while the parts inside have no form of corrosion mitigation and made from cheep materials so it does rust. But it appears that if you keep running it on a regular basis it keeps the thing covered in oil and mitigates it. But if you leave one of these things sitting for a long time they might seize up. I tried to free one of those up by giving it plenty of mechanical whacks, feeding it more voltage, pulsing the power, turning it over using compressed air... etc but to no avail.
amyk:

--- Quote from: BradC on March 29, 2021, 05:10:27 am ---With the newer refrigerants and oils a bit of moisture starts to hydrolyze the oil and refrigerant leading to acid, and the rot starts from there.
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POE oil, yes. Definitely do not leave that in there and change it over to a mineral type if you're converting a compressor to pump air.
davelectronic:
I've bought some polyoester oil ISO 64 I found a data sheet for these compressors, but oil quantity isn't on there. I guesstimate around 250ml, going by a Bambi compressor video first use oil fill. That compressor took 500ml but it's much bigger than the 1/6 hp units I have. If it starts spitting oil, then I will empty it and lower the quantity. It's tricky to work out exactly how much is needed. I know the oil pick up is at the bottom end of the rotor, I'm not adding an oil site glass, any oil loss will show up in a water / oil filter trap. I can just measure any oil loss, if I had access to welding equipment I would probably open it up and add an oil site glass and filling port. I've removed the piston compressor from a brand new unit, just be happy to get it up and running with these pair of hematically sealed compressors. I should get a reasonable duty cycle with a 24 litre receiver pressurised to 8 bar, I had detected a small leak before dismantling the original noisy compressor. Acquired some loctite thread sealer, so will dismantle and reassemble the pipe work and fittings.
BradC:

--- Quote from: davelectronic on March 30, 2021, 01:27:56 pm ---I've bought some polyoester oil ISO 64 I found a data sheet for these compressors, but oil quantity isn't on.

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Take it back. It’s terribly hygroscopic and will just turn to acid. Flush it out and replace it with plain old mineral or synthetic air compressor oil. I’d use 4GS but that’s only because I have some. Pretty much any light mineral oil will do.
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