Air Distribution

This is an utter waste of power. Use the minimum tank and line pressure needed to achieve the pressure, volume, and regulation needed at the tool(s).

Regulating 160 to 90 at the tool turns (160-90)/160 = 44 percent of the compressor's power into waste heat.

The cost of a compressor is mostly in the electric power input, not the capital cost of the unit, so this "extending the life" with higher tank and line pressures is false economy.

Reply to
Richard J Kinch
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Think of your air system as a battery. When it pumps up to (a charge) of 160# and turns off nothing is lost.

When you use part of the charge for air motors, etc. you only use the portion going through your device. Nothing is lost.

Perhaps you're thinking of a system that pumps to a reservior past a pressure relief valve to a hydraulic tank; an air system doesn't work this way.

dennis in nca

Reply to
rigger

"A sane practice is that for expensive machines that do not tolerate various particles, to install an air filter right on them. Ergo, that's what my plasma cutter does."

It would be difficult to add a filter after every junction. But careful attention to detail works as well.

dennis in nca

Reply to
rigger

Rigger, this is untrue and Richard Kinch is correct within his set of assumptions (which probably do not apply to your home shop).

If you use a given amount of energy (such as 1 kilowatt-hour) to compress air to 120 PSI, you can then use that air to power your air tools and get back some good fraction of that energy.

If you use the same 1 kilowatt-hour to compress air to higher pressure, such as 175 PSI, you will get less energy out of your tools.

This is because compressing air to higher pressure heats air more than compressing air to lower pressure, and that heat is completely wasted (unless you are also heating your shop in winter, for example).

So it is indeed true that compressing air to more than the required pressure wastes energy. And it is partly a reason for rotary screw compressors.

However, many "home shop" owners do not particularly care about the cost of energy, as they use their compressors very little, say an hour per week. A more important issue for them could be availability of a lot of air for short bursts of air use. And under these circumstances, maintaining a higher pressure makes sense.

Energy is lost when compressing and heating.

i

Reply to
Ignoramus26567

I use that idea for air, water, and coolant. When available, we use crossing tee's. Also known as a cross depending on were you live.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Reply to
Wes

(snip)

I kinda think of this as "if the customer wants to kill themselves on a piece of equipment, _they_ can build it".

Orderliness as a virtue? If that's not a mistranslation, I'm doomed!

Reply to
Tim Wescott

"Ignoramus26567" wrote: (clip) This is because compressing air to higher pressure heats air more than

^^^^^^^^^^^^^^^^^^^^^^ Dropping the pressure to a lower value through a throttling valve or regulator wastes the energy that could have been obtained by running it through an air motor to lower the pressure. So you lose on the way up and you lose on the way down.

Reply to
Leo Lichtman

Use galvanized to an air filter, with brass or copper from there to the QD. Put air filters on the "important" stuff.

Reply to
clare

Great point.

Reply to
Ignoramus26567

As others have already said, very bad idea, the pressure listed on the pipe is liquid pressure, which is a very different animal, (thus the reason hydro testing uses water for pressure testing) a very small amount of non-compressible water has to leak before the pressure falls to zero, not so with gases.

If you feel compelled to use plastic, ABS is rated for gas pressure.

Stuart

Reply to
Stuart Wheaton

Let the Record show that Gunner Asch on or about Tue, 10 Mar 2009 11:47:04 -0700 did write/type or cause to appear in rec.crafts.metalworking the following:

Sounds like a shop which was plumbed for air with PVC pipe is like the guy who was told smoking cigarettes was bad for his health. "I don't know, they haven't killed me yet."

tschus pyotr

- pyotr filipivich We will drink no whiskey before its nine. It's eight fifty eight. Close enough!

Reply to
pyotr filipivich

I don't recommend it, I have switched to PEX for impact resilience, but I have at least 100' of 1/2 and 3/4 white PVC that is at least 25 years old, without issue.

Reply to
Elliot G

All this discussion got me curious about the relative strength of copper vs. black steel pipe. As I suspected, the black pipe is stronger. 1/2" black schedule 40 is rated at 10,380 psi bursting pressure, while 1/2" Type L copper (hard) is rated for 4,600 psi bursting pressure.

Reply to
Jedd Haas

Uh, actually, not. Throttling doesn't affect the pressure-volume product. No energy is lost by throttling. However, expansion of the air to a lower-pressure downstream value does give up heat upon expansion. Whether that "loses" energy depends on what the temperature of the air was before it was throttled, and what it is just before you actually use it to perform some work. It can regain that energy from the ambient heat in the room, if the expansion dropped the temperature of the air below room temperature when it expanded, and then the air re-heated by running through the copper pipe in a relatively warmer room.

Running that same air through a motor results in a greater PV loss -- lower pressure or less volume -- than it would through a throttle that produced either the same downstream pressure, OR the same downstream volume. The difference is the work performed by the motor.

Most of the energy loss is from what you suggested in the first place: losing the heat of compression. That's why those compressed-air cars they've been experimenting with in France are so inherently inefficient. You can, in theory, recover all of that heat. But it's like recovering lost heat in a steam engine or turbine: exceedingly complicated, with multiple heat exchangers.

-- Ed Huntress

Reply to
Ed Huntress

Not sure what you mean by "throttling".

Energy is certainly lost in dropping pressure via a regulator. The entire pressure drop (times volume) is wasted. It has nothing to do with the heat contained in the compressed air itself. This should be obvious from conservation of energy. But shop air users can be quite stubbornly ignorant of physics.

Reply to
Richard J Kinch

Aside from safety issues, my use of the PVC's was some years ago when it was "new", and with a specific electric conduit called "Septre", and to run control wires in a hoistway.. Worked nice, easy to use and bend. But two months later we had to back in and triple up on the number of wall clips to stop the sagging in any of the horizontal runs over 3 feet. It was in a fairly warm area in a meat packing plant.

I would also like to congratulate the RCM community for over 30 straight emails that didn't wander off topic!!! PLEASE...NO REPLY TO THAT COMMENT!!!

Brian Lawson, Bothwell, Ontario.

Reply to
Brian Lawson

My shop is all galv steel. 3/4" main with 3/4 x3/4 x 1/2 tee's all pointing straight up, two 90 deg street ells to turn it down the wall

90 deg ell out from wall then a ball valve and a QC coupler. no drip legs anywhere, never had water anywhere except in the compressor tank.

All Milton type "A" QC's, you can just push to connect without pulling back the collar. Very nice feature.

CNC machine has a built in filter/oiler/regulator. And I have a filter/oiler that I plug in where needed.

Champion compressor 5hp 80 gal., 175 PSI. Located on other side of wall in the unheated warehouse side of my building.

I held the pipe in my lathe and used a Ridgid pipe theader head to thread it. ( model 00-R)

If you do use copper, you might want to use a few steel nipples and ell's at the end of each leg. My uncle did his garage in copper, tripped over a hose and bent the hell out of the copper tubing.

Thank You, Randy

Remove 333 from email address to reply.

Reply to
Randy

Maybe that's because the ones that did have a problem are now 6 feet under.

Reply to
Mike Henry

On Wed, 11 Mar 2009 09:03:18 -0500, the infamous "Mike Henry" scrawled the following:

Whadda maroon! I've worked in shops (new, inspected/stamped-off in '83) with PVC air-lines and have seen the fittings and lines break from damage when a chain pull let loose or when someone drove off with a hose in the door. Nobody was ever hurt from the "horrible shrapnel" of the "exploding PVC" you guys seem to worry about. Can you cite a death report, Mikey? OSHA only shows one lacerated hand.

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BUT, I've read the OSHA warnings and I wouldn't use Sch 40 in a new shop. HF has 100' PVC-jacketed hose for ten bucks. Why use hard lines at all, unless you have multiple taps going balls-out at the same time? ABS is approved if one wants to save money. Just don't hit it with anything while it's pressured up...

...or you'll be SIX FEET UNDER, right, Mikey?

-- I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them. --Thomas Jefferson

Reply to
Larry Jaques

I use flexible hose as well for my "shop air".

It is safe, easy to work with, and cheap. Very easy to splice when necessary.

If it ever ruptures because or something, all I will get is a loud PSSSSS6666SSSSSSSST.

Reply to
Ignoramus11158

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