On Sat, 7 Apr 2012 19:52:52 -0700 (PDT), rangerssuck
wrote:

On Apr 7, 10:41*pm, "Steve B" wrote:
I'm interested in building a surface supplied air compressor for two divers.
22 cfm@150 psi. *I know that the big difference is vegetable oil in the
crankcase vs. petroleum based oil, but just wondering if anyone had any
experience with this. *A new one especially made for diving is going to run
about $7500, and one could be put together from components for less,
provided the air generating part is compatible with breathing air.

Anyone?

Steve

Just guessing here, but I imagine that a large part of that $7500 is
going to lawyers and product liability insurance companies. Are you
building this for someone who will NEVER sue you? You may want to
think about consulting with a lawyer and an insurance broker before
you get too involved with this project.

That said, have you looked at used and/or surplus equipment? A quick
glance at Google turned up a bunch of stuff - much oif it is SCUBA
(5000 psi), but there are definitely some diving compressors out
there.
One of the big problems with compressors used for breathing air is
carbon monoxide. Temperatures can be high enough for CO to be formed
in tiny amounts. When CO is breathed it sticks to hemoglobin better
than oxygen so it builds up in the blood. Besides being a poison in
itself it also displaces oxygen in the blood. So even tiny amounts can
eventually kill you. At depth the partial pressure goes up so the CO
is absorbed even faster. The filters used with breathing air
compressors remove CO along with other contaminants. Having
experienced bad air once from a dive shop I wouldn't risk a DIY
compressor.
Eric