Machinist's Workshop Article

Expansion and cooling.

Bernd

This is commonly done to act as a heat exchanger. The hot air leaving the compressor is cooled somewhat by being passed through the copper tube where some of the heat is radiated to the air. Presumably this cools the air enough so that the water vapor contained in it turns to little drops which can be collected by a filter. I always thought of putting a copper coil in a bucket of water, into which one or more bags of ice could be dumped for peak need if necessary. Perhaps a coil in ambient air would be enough.

I thought his construction (the coil mounted up under a workbench) was well done, and the article was well done and interesting too.

GWE

I used to ride bikes (dirt) with a machinist named John Hall...??

Jack

"John Hall" wrote in news:mIfGd.211009$ snipped-for-privacy@ursa-nb00s0.nbnet.nb.ca:

It is used as a cooling coil for the air, to aid in water removal/condensation.

OK, I understand the cooling, but still wonder if this is overkill. Why don't any of the shops I have been in need to do this? My compressor does collect water, which I drain periodically from the tank. I use it for painting and driving nailers. When I use it, it's working steady. I never sensed there was a problem. Is cooling of the air that big a deal?

John

Nope. just another one of the thousands of us.

John

Some geographical locations have air that contains much more moisture than others. Also, some guys have applications that are much more moisture-sensitive than others. If you want to spray paint, for example, you need *dry* air.

If you blow air do you see a mist of water? If you direct the stream against a piece of metal plate, do you see water "piling up"? If so, then you have a lot of water in your air.

GWE

Here in the Central Valley of California, during the summer months, I drain my compressor maybe once a month, sometimes even less. I go to Newport Beach or similar places to service machines, and the guys are using the air hoses like squirt guns, spraying long streams of water.

Climate makes a HUGE difference.

Gunner

"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke

We have refrigerated drier systems through which we pump the pneumatic control air for the building(s). Different application, same principle.

(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

I missed the staff meeting but the minutes show Gunner wrote back on Sun, 16 Jan 2005 05:01:27 GMT in rec.crafts.metalworking :

And sometimes, mist when you blow off the part is the sign you need to go double check the blasted "automatic" drain on the tank. And check the various water traps. And then come back and drain the air line.

Oh yeah.

I haven't read the article, but I have quite a bit of experience installing copper air systems. My personal system is 3/4" and over

200 ft of tubing (shop is 38x26). I've read the advice from TP Tools that says you should only use black iron but respectfully disagree. Their concern is that a soldered joint might separate under pressure - the soldered surface area is over 1" sq. I have yet to have one come apart at 125 or 175 psi and I've been running them for years. Note: Use a flexible connection between any air system and the compressor to isolate compressor vibration from the piping system.

When air is compressed the temperature rises (aka PV=nRT) and so does the amount of entrained water vapor. The purpose of a long run between the compressor and the outlet is to provide air travel distance allowing the heated air to cool. As the air cools the water vapor condenses. Copper is an excellent conductor and is perfect for this purpose. The piping should be running slightly uphill away from the compressor allowing the water to run back away from the outlet. Usually drops are provided in the piping system to catch water with valves at the bottom to drain the system. Think of the anti-water hammer risers in your home, but in reverse - pointing down instead of up. The system I installed in my shop has 7 such drains plumbed out through the walls so I can just crack the valves and drain each collection point.

The copper coil you reference is probably in the system to add cooling distance in a relatively small amount of space. A coil can also be placed inside a refrigerator or in an ice chest to provide a larger temperature differential to speed condensation. This is also how commercial air drying systems work - they are heat exchangers removing the heat from the high pressure compressed air side and dumping it into the environment. A coil also works well to "sling" the water out of the air stream as it condenses - takes advantage of angular velocity.

Any air system should have a water separator and a filter at the end of the stream. No matter the pipe selected you will get particles in the compressed air that can contaminate your air tools, especially painting.

Ryan Reid Systems Eng>Just got the Dec/Jan Copy . In the article titled"Shop compressed air for in

I'm not so sure about the water flinging to the sides of the coils as the air travels through it. I do know that having the pipe cool the air is good. Also, the larger the pipe the better. This is because the larger pipe lowers the velocity of the air. Fast moving air will pick up water that's on the bottom of the pipe. At the spots where you tap the pipe for air a tee should be installed with the outlet UP. Then, use a U shaped of pipe to bring the air down to the shop. Having the air outlets on the top of the pipe helps to prevent water from becoming entrained in the air. ERS