Breathing Compressor Oil characteristics

[phgachoud]

Bought a coltri MCH6. Air filter was changed 1 year ago and used for a few minutes only. On the first fill of my tanks the air was wierd. Am waiting for a replacement cartidge, but takes it time to get here in south america .

Filling my tanks and specially after when turning off the compressor, I saw some fumes getting out of the intake tube (I put 2m higher with a plastic tube not as the pictures you are about to see...).

I was worried that those fumes go into my tanks and of course my lungs as much. Dove my tanks for more than 1h30 in the water and didnt get dizzy so looks like am not dead and working ok. I know I should analyze my air, but its not easy to get that kind of services out here...

Seing those fumes after stopping the compressor each time, I was wondering about the compressor construction and what are the lubricating oil specifications making that there is some oil going into the air the compressor absorbs, and then probably and hopefully is filtered by the filter before going into the tanks and lungs... which makes me also think of course of filter saturation level of those.

So, my understanding is that in the img above (removed the oil cap/gauge) the green tube between B and A is meant for the differences of pressure caused by the movements of the pistons to let some air interchange outside the motor, which is also the case in thermic motors (dont have the technical word for that in english). That makes sense for me in a mechanical manner, but! what about the oil getting out of it getting drained direcly into the inlet of the first piston making the oil and fumes mix with my breathing gas!!! Making me think that the oil is special enough to be not that bad in terms of healthyness or is the after compression filter guarantying that? and to what extend, knowing my current filter is probably more than 1 year old and the active carbon might be less efficient or dead.

So the big Q is, is a breathing compressor oil that special its breathable even after having been mixed with air and sometimes heated!?

For more illustration, here is where the green tube goes into the first piston through the air inlet (removed for the picture so you can see where it goes). Air comes from the blue tube, green tube's oil finishes into C as well as the tube

Thx guys!

 

[tbone1004]

in oiled compressors there will always be some oil that ends up in the breathing gas. If the compressor is functioning properly AND the filtration/water traps are designed properly, none of it should end up in the gas that goes to the tanks. There will be interstage water traps where most of the oil will be knocked out along with the water mechanically and blown out during the purge cycles. If you put a catch-can under them and let it sit for a few minutes you will see the oil separate, it will be a very small amount of oil, but there will be some. The rest that doesn't get removed mechanically is separated out by the filter cartridges. It is preferred to use synthetic oil designed for breathing gas, but that is mainly from an oxygen compatibility standpoint and other types of oils were/are used for many decades without issue.
I wouldn't imagine seeing an actual puff of smoke or anything out of the intake under normal circumstances, but if you need a ring job in the pump it's possible that there is a lot of blow-by from one of the stages and could manifest that way. If the pump hasn't been used in a year it may just be some stuck rings and after a few hours of running it will break itself loose, not dissimilar to a combustion engine

 

[Mudbags]

Great information from @tbone1004 - a small amount of oil will always carry over into the air. It's the role of the oil/water separators and final filter to remove the oil residue. In most countries/areas it's acceptable for a very small trace amount of oil to be in the air but it's very important that you can't smell it. Make sure you smell the air in your cylinder before you go diving with it.

The green tube on your photo is a crankcase breather. When the piston rings start to become worn, more and more air will pass the rings from one of the 3-4 stages and make its way into the crankcase (this is called blow-by). The crankcase breather takes that air and feeds it back into the air intake/first stage of the compressor and the air goes through the compression process again. Compressor crankcases are not designed to hold pressure so the breather line is required to prevent pressure buildup.

This also explains the 'puff' you see when you turn the compressor off. The residual air in the crankcase is venting through the air intake.

Be vigilant with your filter changes and consider inspection and replacement of the piston rings.

 

[Namreg 58]

Because you have a reed valve plate on the first stage the oily blowby is designed to lubricate the reed valves by design. This system is used on many brands of compressors, not just Coltri.

 

[dead dog]

" I saw some fumes getting out of the intake tube" - Lite a match to the fumes coming out, this is called "Burn Off".