Diameter of air lines

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My stationary air compressor has a 1/2" NPT fitting for the output.
I will be using copper pipe for my air piping. Should I use 1/2" or 3/4" copper pipe for my main lines? The internal diameter of 1/2" copper pipe seems awful small. (Yes, industry does use copper for air piping.)
Brian Elfert
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If I needed to supply 8 CFM at 100 PSI, would 1/2" copper be good enough?
Seperate issue:
Could I run compressed air 100 feet underground to a shed and still get 8 CFM at 100 PSI? I'm trying to figure out if I need to buy a seperate compressor.
Brian Elfert
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Probably not, due to a phenomenon known as head loss. However, you might be able to put an air tank on the end of the line in the shed, and get acceptable intermittent performance.
-- Howard Lee Harkness Texas Certified Concealed Handgun Instructor www.CHL-TX.com snipped-for-privacy@CHL-TX.com Low-cost Domain Registration and Hosting! www.Texas-Domains.com
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forth from the murky depths:

100' of 1/2" Sch40 steel pipe is good for 15cfm according to the chart on Pg 632 of my Lee Valley copy of Handyman In-Your-Pocket. 0.2500cfs
========================================================= I drank WHAT? + http://www.diversify.com --Socrates + Web Application Programming
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Brian, A word of caution, 100' of air line underground will trap and collect a ton of water. If you must install it under ground, slope it the same as you would a sewer line. At the end (low side) of the line build in a drip leg and a way to discharge the water. A sperate smaller reserve air tank wil go a long way to help with head loss.
Dave
writes:

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Good point. Consider a separator before the line goes underground. There are cartridge type filters available. Ed
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How does a seperator differ from a normal filter, or is this just another name for a filter? The best option would probably be a drier, but another compressor is less money.
Brian Elfert
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I was wondering about that. I suppose I would have problems with the line freezing in the winter, as it gets way below 32F here. I have to run the line exposed 1/4 of the way as I'm not going to tunnel under the basement foundation and the garage.
I thought if I put a good dessicant filter on the line I might be okay, but thinking about it more, the cold will cause water to condense out of the air.
I'm starting to think another compressor in the shed might be my best option.
Brian Elfert
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Brian Elfert wrote:

No no no no no ... nononono
God, No. >>>>
That's what went through my mind when I read this.
Use a standard separator, not a separator/ filter, certainly not a desiccant, where the air line comes out of the ground. And make it a big separator. The condensate will lay in the line and the air will gurgle through it bringing up droplets or until there is enough water to come out in a surge. You'll need something big enough to catch it.
Don't use a desiccant drier as the first thing on the pipe unless your into water soaked desiccant from the above stated reasons. If you did you better have a very forgiving wife who doesn't mind having the desiccant baked in her oven. Allot. Using a drier is a great idea but you need something to catch water mass first.
I would suggest also putting a 'T' in the line after the ground and before the air enters the separator and putting a ball valve on it. That way when the line fills with water you can blow out the line. It should be standard practice to blow the line before and after every period of use.
As long as the line slopes down until the low point is a couple of feet under ground I would guess freezing shouldn't be a problem. OTOH I can see where vapor would condense on the surface of initial few feet of line above ground, depending on how bad assed cold your neck of the woods gets.

That has it's own issues.
--
Mark

N.E. Ohio
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A larger diameter will provide more volume transfer and faster recovery. That may or may not be important, depending on what tools you plan to use. If you are not sure, use the 3/4".
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I used 1/2" copper and it works fine.
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Brian wrote:
Group: rec.woodworking Date: Sun, Dec 21, 2003, 8:00pm (EST+5) From: snipped-for-privacy@visi.com (BrianElfert) My stationary air compressor has a 1/2" NPT fitting for the output. I will be using copper pipe for my air piping. Should I use 1/2" or 3/4" copper pipe for my main lines? The internal diameter of 1/2" copper pipe seems awful small. (Yes, industry does use copper for air piping.) Brian Elfert ****************************************************** Please use soft copper tubing and compression fittings no matter what size you choose. Black iron pipe with threaded fittings is also extensively used but requires a pipe cutter and a stock and die. Do not use hard copper tubing and sweated (soldered) fittings. This suggestion is made for obvious safety reasons.
Peace ~ Sir Edgar
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I HOPE there's not a safety issue with using sweated copper for air .. .. .. I just plumbed my whole shop with it !! !! !!
What's the danger ?? ?? ??
Sir Edgar wrote:

-- I AM NOT PARANOID .. .. .. but EVERYONE thinks I am !! !! !!
<<<__ Bob __>>>
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<<<___ Bob ___>>> thus spake:

Not NEAR the danger of using PVC. Copper generally splits open, PVC explodes - sending near supersonic shrapnel everywhere.
Greg G.
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I have always heard this but I would sure like to see someone demonstrate it. I tried to make a big firecracker with 1/2" PVC and smokless powder when I was young and dumb. It just split open and none of it really turned to shrapnel. That was a lot more than 100PSI. I imagine a decent spud gun is above 100PSI and we don't hear about them > sending near supersonic

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Greg thus spake:

All I can relate is the story of a friend who owns a print shop. They have large presses and such that are larger than a bus. He decided to go cheap and install 3/4" PVC pipe for the air feeds - standard 120psi air supply. It exploded several times in various places until he ripped it out and replaced it with copper because a worker was sent to the ER because of flying plastic. I believe it involves long term fatigue cracks in the pipe. OSHA has published several booklets on the how's and why's of NOT using PVC for air supplies.
Greg G.
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I know this is the rule and the reasons why PVC might be dangerous, I just don't understand how 120PSI can make 470 lb rated PVC "suddenly explode".
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PVC is a lot different than other nonplastic materials Ratings for liquid that it is designed to carry is different that compressed gasses. Liquid at 470 psi is not going to expand very much at all, but a gas (like air) will expand in volume greatly when released.
Copper or iron pipe does not shatter like plastics. They may leak but will crack or pin hole. Plastic just "lets go" when stressed.
The stresses can be different also. Plastic will degrade from UV exposure Plastic can become brittle and break like glass, and that is the biggest problem.. Ed
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