What's the problem with mineral oil?

Guy Manners · May 30, 2011

before you all go off shaking your heads at this old topic, bear with me. I know the reasoning behind Synthetic oil for compressors that are used for filling Nitrox tanks, most important if topping up or continuous blending - the compressed air is smacking into a tank full of compressed O2.
SO for safety's sake, we use a synthetic oil which... errmmm... has a higher flash point? Or what? I've been hearing as well, recently, that if you change over from Mineral to Synthetic, you have to take the compressor apart & clean it with a toothbrush to get all the mineral oil out.
The air that comes out of the compressor is full of oil vapour, water vapour etc anyway. So I've got 2 big expensive filters (where 1 meets UK standards for normal breathing air...) between the compressor and the tanks; Why can't they handle whatever the problem might be?:confused6:

Guy Manners · May 30, 2011

, sorry all, I guess I found it. If you use continuous blend, the copressor is getting a higher O2 %age into the intake - so all bets are off, it's gotta be right. I partial pressure mixing, the air is already filtered before it hits the O2.
Do I gottit?

iain/hsm · May 30, 2011

IMHO There is no "safety" in using synthetic dieters, trimester or polyalphaolefins, in a breathing air compressor save for the additional 60 odd degrees of autoignition temperature, and thats about as good as a hot cup of coffee.

No. Synthetics are only good for one thing, to extending the mechanical life of the pump components and when operating at lower air temperatures below say 15 degC where a mineral 5-10wt oil would struggle.

Not withstanding the demand in some areas of use (fire departments) to remove all philates from these synthetic lubricants, due to the carcinogen agents being some 500 times greater than allowable in PVC

Frankly Nitrox was never the reason for using synthetics.

What they were designed for purely and singularly was mechanical life extension.

Divers and Nitrox were not even in the considerations.

Best advise is read the label on the pump, it probably just say's AIR compressor.

rjack321 · May 31, 2011

Guy Manners:
The air that comes out of the compressor is full of oil vapour, water vapour etc anyway. So I've got 2 big expensive filters (where 1 meets UK standards for normal breathing air...) between the compressor and the tanks; Why can't they handle whatever the problem might be?:confused6:

Because the problem with mineral oils is partial combustion. Combustion can occur in hot climates or poor installations with normal air not just nitrox. And CO is the big contaminant to be concerned about and its incredibly toxic even at the 10 part per million range. Yes good filters (with catalyst) can handle small amounts of it. But why not make as little CO as possible in the first place?

There is no good reason to be using mineral oils in compressors anymore. Yes, you need to clean the valves and other interior components of previous carbon deposits, this may or may not require disassembly depending on compressor age.

Ian, you really should have a disclosure of your employer in your signature.

Guy Manners · Jun 6, 2011

iain/hsm:
IMHO There is no "safety" in using synthetic dieters, trimester or polyalphaolefins, in a breathing air compressor save for the additional 60 odd degrees of autoignition temperature, and thats about as good as a hot cup of coffee.

No. Synthetics are only good for one thing, to extending the mechanical life of the pump components and when operating at lower air temperatures below say 15 degC where a mineral 5-10wt oil would struggle.

Not withstanding the demand in some areas of use (fire departments) to remove all philates from these synthetic lubricants, due to the carcinogen agents being some 500 times greater than allowable in PVC

Frankly Nitrox was never the reason for using synthetics.

What they were designed for purely and singularly was mechanical life extension. Aren't you getting "designed for" and "use" a bit mixed up here?

Divers and Nitrox were not even in the considerations.

Best advise is read the label on the pump, it probably just say's AIR compressor.

All compressors except one Coltri say "for Air only" but everyone uses them for up to 40 or 50% constand blend. It's just a legal thing. But that's the reason for mineral oil, isn't it? Less chance of combustion and thus CO production??

Guy Manners · Jun 6, 2011

Thanks for this; I'm a bit fed up with the "a sod it it'll be alright" attitude.
There's normally a reason for anything that's generally accepted.
Ian - the extra 60degress, is also the difference - infact, much more than - between the tropics and Shetland. And most will agree, the tropics are more liable to such probelms. Hmmmm?

rjack321 · Jun 6, 2011

If you are going to change, I'd suggest chemlube 800.

The chemlube 751 is ok, its what I have been using since the compressor came that way and it seems to be working for me (5yrs now). But its not that hot here in the Seattle area and I have dual filters too. There's some question of 751's cross contamination with phthalate esters, although my personal opinion is that the AC will have no issue removing those and background exposures for other vinyl products dwarfs any exposure I might have from oil vapors getting past the AC bed anyway. I do make a concious decision to change my primary filter at the same time I change my oil which is every 40-60hrs on so.

What's the problem with mineral oil?

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