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I like using 1/2" copper pipe for compressed air, although galvanized is
traditional. Don't use PVC for compressed air.

Best regards,
Bob

Just before Christmas I went to a tire shop and all of their air lines were
schedule 40 PVC.
This system is pressurized during working hours only. I remarked on the
installation to the owner and he said that it was put in just for temporary
4 years ago. Now he fails to see why he should change it. This was the first
installation of pvc for air that I have ever seen.
They were running 90 psi and all 3/4 pipe