I found the reason for the problem I had in filling the Robart system with the "air fill valve." The needle valve was screwed way too far into the cylinder. The air compressor's fill valve could not reach the needle valve and push it in, so that the air could flow.

Simple problem, but it was too simple for me to look at that possibility. I hope this saves someone else some time and frustration. Just screw the needle valve in or out as needed to make it work.

Jim K.