Air Distribution

Now you've done it, Leo. The only thing more divisive than gun rights on RCM is the thermodynamics of compressible gases.

"Richard J Kinch" wrote: Not sure what you mean by "throttling". (clip) ^^^^^^^^^^^^^^^^^^^ Throttling is the process of lowering the pressure by friction. The energy lost in the expansion is converted to heat. This occurs in valves, regulators and the *throttle* of a carburetor.

Yet.

And I. When I did mine, HF had 25' of 3/8 rubber hose for $3.50! Poor quality, to be sure (a few aneurysms had to be cut out). My "piping" snakes up and around and over in a semi finished basement where hard piping would have been an incredible bitch to install.

As usual YMMV, Bob

Is your statement mostly conjecture? Or do you have the math to back it up?

After 20+ years of working with customers, air dist- tribution vendors and compressor manufacturers I found everyone agreed this (once past the cost of the better piping) is by far the most economical way to operate..

I'll agree, a small home shop will show little benefit but really now, how many home shops have a screw type compressor?? The idea of pumping up your air system pre-dates those machines. Some people like to run as efficently as possible and saving, even a little, is fine with me.

If anyone has more detailed info I'd like to hear it.

dennis in nca

heat is completely wasted

"Dropping the pressure to a lower value through a throttling valve or regulator wastes the energy that could have been obtained by......"

No modern regulator I'm aware of wastes power the way you describe. Do you have evidence this is true (?), perhaps a manufacturers brochure or a pneumatic text??

dennis in nca

And in addition, if you have a compressor heating the air this is the reason for running an "after-cooler" before a "refrigerated air dryer" (available at HF I think) in order to "lower" the humidity carrying capacity of the air.

This system (or a dessicant system) should be used in front of any line used to operate a machine you intend to operate on air pressure. NOTE: You still should install a F-F-R-L at the machine.

Of course, if clean dry air is not an issue because you only use air for blowing off chips, then just go for it using the typical shop practices.

dennis in nca

" But shop air users can be quite stubbornly ignorant of physics."

AND of how regulators operate. Hint: not by "throttling" like a needle valve, but using a diaphram and poppet type valve.

Just go to any manufacturers site which contains info. and all will be revealed.

dennis in nca

Either one works fine. But if you can stand the pain involved when you pry open your wallet, use the Copper. You will hanve much less crap in your air - Steel rusts, galvanizing flakes, and then the rust and zinc flakes and etc. get carried to places you don't want them.

Myself, I silver-braze the lines so some brain dead plumber goes "Waitaminit, maybe that isn't the water line..." But you can use the same pipe hangers and insulators.

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In black steel pipe, absolutely. Plugs are cheap, and a tee is only a few pennies more than an elbow.

Build your natural gas lines the same way, plus go one or two sizes over what you think you need. Because you'll always end up adding something later, and you'll need the extra flow capacity.

In Copper pipe it's not a huge deal to un-sweat an elbow and sweat in a tee, but the more important part is to plan ahead for the eventual expansion. No battle plan survives intact past the first fired shot, and shop layout plans are the same.

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"rigger" wrote: (clip) No modern regulator I'm aware of wastes power the way you describe. Do you have evidence this is true (?), (clip) ^^^^^^^^^^^^^^^^^^^^^ My evidence is simple science. Conservation of energy. When you pass a gas through a device to lower its pressure, there are three ways the energy can go: 1.) It can do work by running a motor or pushing a piston, 2.) It can accelerate through a nozzle, turning the stored pressure energy into kinetic energy (the gas accelerates in the nozzle, 3.) The energy is turned into heat in the throttling process. Since a regulator does not employ process 1.) or 2.), it must turn the energy into heat. QED.

Nope. You were closer when you mentioned entropy.

I had to take a test the other day and it asked what the safety factor on pneumatics should be.

When I buy a component with a rating, do I put a factor on that or is the factor included in the rating?

I thought it was a BS question.

Now as to the OP, every place where I've seen discussion of compressed air and PVC the conscensus seems to be bad, bad, bad.

I'm willing to learn something so I posted.

Wes

Nonsense. Both lower pressure by restriction. The energy of the pressure differential times the mass flow is utterly wasted in any such regulator. Any other notion is just ignorant, medieval superstition. Your sort of thinking is what shows up as perpetual motion machines at the patent office.

The perfect electronic analogy is a three-terminal voltage regulator, which wastes all excess voltage as heat. This is exactly how an air regulator works, dumping all excess pressure as heat.

Perhaps you are confused because the waste heat is entrained in the downstream air, where you don't "feel" it.

Yeah ... I don't know about entropy, but I do know that when a gas expands, it /cools/ (or we wouldn't have refrigerators). The energy must go somewhere, but damned if I know where.

Bob

Funny I've NEVER felt a hot air regulator. Usually they are cold from the refrigeration effect of pressure reduction. I always ran the shop air in the automotive service center at 150PSI

Umm.... no. The easily observed fact that regulators don't get hot should be a hint that this is wrong. Throttles work by an application of Bernoulli's principle; it's just a matter of the relative areas. There isn't *zero* friction, of course, but it's a decidedly second-order effect.

The energy in a compressed gas is used in expanding the gas (as you'd expect), and its temperature is lowered as a result (pv=nrt). Conservation of energy is only an effect in a closed system: a closed system in which you put energy into the gas when compressing it (raising its temperature), and recover the energy as it expands (lowering its temperature) is perfectly valid. There's no requirement that anything go into heat while the gas is expanding.

aaah, guys??? the equations are well known and have been for over a century - why not consult a thermodynamics text and post the equations for the expansion of gasses