Gary Coffman wrote:
On Sun, 28 Dec 2003 23:56:33 -0500, Ned Simmons
wrote:
In article ,
says...
On Sat, 27 Dec 2003 00:50:14 -0600, Richard J Kinch
wrote:


In general, regulation of *any power source* implies an inherent
waste versus the unregulated source: electrical power, compressed
air power, motive power, water behind a dam, etc.

So, if you draw 1 gallon of water a minute through a valve at the
base of a dam, the other 999,999,999,999,999 gallons in the
reservoir are wasted. Obviously not true at all. You use what you
use, the rest stays in the reservoir (with all of its potential
energy intact) until you need it.


Another faulty analogy.

Not an analogy. The man said regulation of *any power source* and
specifically listed "water behind a dam". Not all regulators are shunt
regulators which waste any energy their downstream load does not
demand. Most regulation is obtained simply by not allowing any more
energy than the downstream load requires to be released from the
reservoir, be that water behind a dam, the energy stored in a
flywheel, or the energy stored in a capacitor, or a compressed air
tank.


Since water is essentially
incompressible, the capacity of the water behind a dam to
do mechanical work is almost entirely due to its potential
energy -- its elevation in a gravitational field.

It's easy to demonstrate, without resorting to
thermodynamics, that air expanding thru a regulator loses
some of its capacity to do mechanical work, and that energy
does *not* remain in the air behind the regulator.

It is easy to illustrate that if you're just venting air to
atmosphere, but it is wrong if you're requiring the air to do work
beyond the regulator. The latter is the normal case except when
you're just bleeding down the tank.

The final regulated pressure has to be matched to the task, I don't think
anyone would disagree with that. However, the pressure supplied to the
regulator should allow for some headroom and optimally no more.



Example, assume an air cylinder with a piston surface area of
12 square inches and a stroke of 1 foot. If you feed that cylinder
50 PSI air regulated from a 60 gallon 175 PSI tank, you can do
600 ft-lbs of work by lifting a 600 pound weight the 1 foot stroke
of the cylinder. Now vent the cylinder and fill it again from the
regulated source. You do another 600 ft-lbs of work. Do it again,
and again. You can keep doing it until the pressure in the tank
falls below 50 PSI.

Now try it without the regulator. You can't do it as many times,
because energy stored in the tank has been *wasted* at each fill,
ie the pressure in the cylinder and tank equalize each time you
open the fill valve even though that's more energy than you *need*
to lift the weight one foot, and that excess energy is lost when you
vent the cylinder. This is a clear case where the *absence* of a
regulator wastes energy. It is in fact the *usual* case.

Gary

I don't think anybody is arguing against the use of regulators. The point
that a few of us have been trying to make is that x liters of air at y
pressure can do more work than 2x liters of air at y/2 pressure. Double the
pressure and you double both the force and the distance that the force can
be applied, in the case of the piston that Ned cited. The original post
surmised that a regulator was analogous to a transformer. It's not. A gas
regulator also cannot be compared to regulating water from a tank.