[Al Skierkiewicz]

James,
I checked our ViAir last night and the check valve is mounted directly to the compressor. It has a nice arrow punched into the body. The additional fitting appears to the transition for supplied check valve. I did not pull ours apart to see what, or if, there is a threaded transition on the check valve. This is certainly a question for the Q&A I think. I like that there is some metal at that port to help cool off the output air. That little compressor does run hot if you run it often.