The volume increase would be too small to matter one way or the other and you will never need the additional flow capability that it would add so in effect you would gain nothing, there would be some small cooling advantage but nothing worth the added cost of the larger pipe.

that's what I was looking for. I'll be running 3/4 for the full length... thanks oldred

I am getting ready to put a new air line system in my garage and wanted to thank all for the great info in this discussion. Hope to eliminate the moisture problems I have in the present system. Thanks again.

I researched this fairly extensively. Steel is ok but not very user freindly with threading and fittings and time to install. I visited several garages,a new wing in an engineering college as well as the Fleet garage at the utility I work at. All of them use copper. I used copper and found it to work very well. No matter what you use remember to use nothing smaller than 3/4" and run not smaller than 1" feeder trunk. You will get good pressure with smaller but you will loose volume (cfm).

I'll be piping my garage in the next month or so. I'm leaning towards 3/4" black pipe, but the outlet of my compressor is 1/2". Should I stick with 1/2" throughout, or should I step it up to 3/4" ?

Just step it up and run 3/4....that way if you ever upgrade to a larger compressor you will have the right size line.

Sounds good.....3/4 it is!!!!!!!

C.