Hobby Air???

I am glad you are thinking about safety. Modern painting materials containing isos can be particularly nasty to use. Check out the fine print on a hardener label :o). Unfortunately many, including myself years ago, just have to learn the hard way.

I have been successfully using a dedicated, non-lubricated, tankless air compressor as a source of breathing air for occaisional painting (using isos) for about 25 years. I have mentioned details about it in a prior post so I am just linking to it here rather than repeating it. I noticed the old link in that post to an "official" but "not agency approved" compressor marketed for that purpose no longer works so here is a current one. As noted, mine is not an "official" compressor for such a purpose but I decided, at least for me, that it was an acceptable risk. It has served me well for a long time.

I would seriously question whether a compressor sized for air brush use had enough capacity for breathing air purposes. You should have 4 cfm minimum for a facepiece or 6 cfm minimum for a hood.

The Hobby-Air system that CN uses is a very popular one for the part-time user; at least that is my impression from all I have heard about it. Since it is sold as a system, one doesn't have to cobble together parts on their own to make a complete, functional, relatively low cost unit. I say relatively low cost because there certainly are other complete packaged systems but all are significantly more than the $500 or so for the Hobby-Air.

3M makes a lot of very good products but I don't particularly agree with them if they say it is OK to use a shop compressor for breathing air if it has a particulate filter. There is more at issue than particulates in using shop air for breathing. Namely oil vapor and potentially carbon monoxide. An "official" package for such use would normally include a carbon "taste and odor" filter to handle oil vapors and a CO monitor/alarm in addition to a particulate filter. There are belt-pack units marketed for that purpose and perhaps 3M also sells one. Although one might want to take the risk of not having a CO monitor/alarm, I have found by past experience that the oil vapor can be a problem. Before I got my dedicated compressor, I tried supplying my full face mask with shop air. I had a distinctive oily "aftertaste" that I found objectionable and decided that I did not want to breathe such stuff. There is also the capacity issue. Unless you have plenty of extra compressor capacity, robbing a full 4 cfm for breathing may make you short of air for supplying a full sized spray gun for any length of time.

I think Butch uses shop air successfully for feeding a mask so he may stop by and provide some info on his experience. I just don't like the idea. I have a personal dislike for taking any kind of air that is not acceptable to breathe and processing it by means of special filters, etc to yield good results. I don't think it is the best approach. Not while there is a reasonable alternative readily available. That reasonable alternative is, IMO, using a source of already clean fresh air supplied to the mask by a system that is not capable of adding any harmful "stuff". That can be accomplished by either a non-lube tankless "compressor" (diaphram or piston type) or a turbine/blower like the Hobby-Air system uses. If you use such a system you should plan on using at least 50 feet of hose to permit locating the compressor/turbine in a known clean air environment.

Rod

At what PSI would you need those CFM numbers?

Only a few psi. As mine is a tankless unit, I completely removed the regulator that came with it (kept the relief valve functional though). The pressure will build up to only that required to provide the cfm flow rate through whatever hose and couplings are being used. I have never put a pressure gage on mine (back at the compressor) but think it is no more than about 10 psi, possibly less. That's with 50 feet total of 3/8" ID standard air hose and three 1/4" quick couplers. I realize most compressors are not rated at that low a discharge pressure. They are usually rated at 90 and sometimes also at 40. A piston type compressor will always have a capacity characteristic that yields a somewhat rising cfm with decreasing discharge pressure. I would estimate that if you had one with a rating of 3 or 3.5 cfm at 90 psig you would do fine since you would be close to the 4 (for a facepiece) with the same machine at the much lower pressure.

I verify that I have enough flow by holding my palm up next to the facepiece exhaust valve and taking a deep breath in normal fashion. As long as I can still detect an outward flow at my palm during this deep breath, I know that the facepiece will always be under a positive pressure with respect to the surroundings and therefore will be satisfactory.

Rod