On Fri, 09 Jan 2004 16:46:45 -0600, Richard J Kinch wrote:
The operating principle of a conventional regulator is a restriction.
It is just a valve with a feedback arrangement on the handle
Restrictions are lossy. Otherwise we'd be using the thinnest possible
air hoses instead of paying for big ones.

Work is not a time function. You can conduct air from a tank to a piston
though either a large pipe, or a restricted pipe. The resulting work done
by the piston is the same, only the rate of doing the work changes.
When doing an energy accounting (change in potential energy vs
work done), rates don't matter.

Air is driven through the aperture of a valve by a force which is the
product of the pressure differential existing across the aperture times
the area of the aperture. A small aperture will necessarily have less
force pushing air through it, and will push less air in a given time. But
that doesn't affect the amount of work the air can do on the load side.

Work isn't a time function. Work is force times distance. How long it
takes is irrelevant. Less work is done pushing air through a small
aperture than through a large one of the same length. In other words,
open the valve fully, no regulation, and more work is required to move
air through the length of the valve than would be required if the valve
were nearly closed.

Of course you move more air per unit time in the former case, but
work isn't a time function, so that's not relevant when calculating
dissipation.

The regulator itself has nearly zero loss, as my example of drawing
down a filled tank to supply a load shows.

I've lost track of who is exhibiting what. But this waving of hands
with Boyle's law and energy being P*V is flawed analysis. It shouldn't
even take analysis. It should be obvious, anything that impedes the
flow of compressed air has got to be robbing power.

Power is expressed at the point work is done. It is the rate of doing
work. P=W/t. There's no work being done by air in a reservoir, so there
is no power there. There is work being done transporting air to the
load, and work done in the load. The latter is the desired work, the
former the parasitic loss. As shown above, a large bore valve/hose/pipe
requires more work to transport air than a small bore regulator/hose/pipe.
So parasitic loss, energy dissipation, is less with the more restricted
system.

You keep confusing power and energy. They aren't the same thing.
Energy is the capacity to do work, or equivalently for accounting
purposes, the amount of work done. Power is just the rate at which
work is done at some point or points in a system. It is a time function,
a rate, energy and work are not.

Gary