On Mon, 12 Jan 2004 15:24:00 -0800, Grant Erwin wrote:
I explicitly phrased my question to state that the only air flow I was
interested in was what went through the regulator, although many many
people took it to mean I wanted to understand how an air compressor works
or what is efficient or inefficient about it. I didn't care in the
slightest about that. If I had it to do over again I would phrase the
question with an imaginary sea god blowing into a tube such that
10 CFM @ 180 psi @ some temp were flowing down the tube, and ask if
that tube went into a regulator and came out at the same temp at 90 psi
how many CFM would be flowing.

You can't answer that question without knowing something about the
downstream load. A regulator works by releasing only enough air to
cause the downstream pressure to rise to the set point. If the downstream
is a sealed tube, flow stops quickly as pressure rises to 90 PSI and remains
there. If the downstream load consumes air, ie does work with it, then the
flow from the regulator increases above zero flow until the amount of air
flow is just sufficient to make up for the load consumption.

So it doesn't matter how large the air mass is above the regulator, or
how much pressure exists before the regulator, the mass of air which
the regulator allows to flow downstream depends solely on the set
pressure and the load demand. The regulator isn't a resistance, it
is a demand controlled valve with a variable area aperture, capable
of opening or closing completely under control of the diaphram, which
is responding to downstream pressure. If you don't know the demand,
you can't know the downstream flow.

Air and its associated energy not needed to meet the demand simply
remains upstream of the regulator, normally in a tank, but in your
Sea God case, in his lungs. It is emphatically *not* dissipated in the
regulator.

Gary