"chaniarts" wrote in message ...

On 2/14/2013 11:12 AM, John Grossbohlin wrote:
"Mike Marlow" wrote in message ...


To set the "right" pressure for the tools we had a gauge on quick
release fittings that could be installed at the tool end of the line.
We'd regulate the pressure to that gauge rather than the gauge on the
regulator on the compressor. That allowed us to regulate the working
pressure in the context of the length and diameter of the hose. Once set
the line gauge could be removed to lighten the tool weight. We had a
regulator with a gauge for the spray gun as that often needed tinkering.

i always thought the pressure at one end of the hose has to be the same at
the other end of the hose, given a static condition. is that not correct?

Static I would agree. In use what we found though was that a small line
cannot recover fast enough so the working pressure drops. This is due to
inadequate volume and friction in the line. Thus with a gauge at the tool
end of a long run you can watch what happens to the pressure while the tool
is working and then set the pressure higher at the compressor end to help
keep the volume and pressure up at the tool end. Larger air lines can help
with the volume and friction issues over long runs...

Air volume, pressure, friction, air turbulence in the lines, compressor
capacity, and other factors are at play and I'm sure someone here can
explain this in fluid dynamic terms. To us layman woodworkers I'd think it's
not unlike the topics of undersized piping in a dust collection system, or
comparing a dust collector to a vacuum cleaner, that have been discussed
here what seems like a few hundred times over the past 20 years. ;~)

John