[Johnp]

The larger diameter pipe would give you more capacity but unless you are going change the outlet on the compressor you really won't be able to take advantage of it. Most I have seen only have 3/4" outlets.

[aj66gto]

Very good point!!!

[Bill Eveland]

I'm putting my compressor in my basement and running an air line to my garage, i'm going to use 1/2 " black pipe - it's about twice the inside diameter size of the inside of a 3/8" air hose . If you have a pretty long run, use the 3/4" black pipe than 1/2" in your garage.

[CDJr]

Bill, I think galvanized is better to use cuz its not as prone to rust from the moisture content.

[Bill Eveland]

Correct , going under ground it would be better to use the galvanized, I was referring to what I was using above ground, black pipe is what we have here at our shop and have never had any problems.
We have a drain at each fitting tee for drainage.
When setting in the pipe in the ground , I would set it at a slight slope to drain back in the house and have a low point made and install a ball valve to drain the condensation out .

[aj66gto]

Bill,

I'm done with the line underground. I used 3/4" Gal. pipe. It went fine. $13 a 10' length. The electricial stuff was $22.

Anyway, I used the plumbing stuff with the fittings. (No bending ) You plumbers got the life.

I did not slope the pipe as I did not know to do that. I have a filter at the compressor that should catch any moisture. If not....,Oh Well. It will take 20 years to rust and I would have moved out of this house by then anyway.

Wish you well,
Anthony

[CDJr]

Actually Anthony, you should definitely have a filter further down the line, closer to where the tools plug in cuz a lot of moisture is created IN the line as the air is cooled, well after it has left the compressor. And its not necessarily to prevent rust, its mostly to protect your tools, as moisture shortens a tools life.

[63RedCat]

DO NOT UNDER ANY CIRCUMSTANCES USE PVC FOR AIR LINE!!!!!

It will fail over some period of time and shatter. I have seen it send pieces of pvc shaped like needles through a 1/2" plywood wall. This is caused by the constant increasing and decreasing of the line pressure. PVC is not designed to handle the stress.

[Tigerpaw65]

DO NOT use PVC under ground with gluded fittings. I used it for the water line to the garage, the glue used on the joints sperated after just over a year at 80psi. A chemist friend told me this happened because of the acids in the earth.I would think the same will happen with sweated copper joints.Go with galvanized 3/4", so you need to thread a few joints. IT's the safest.