Compressor & tank with one port each?

Every diagram I can find showing how to set up a pneumatic system has compressors and tanks with two ports. One port on the compressor, for example, goes to the pressure relief valve, and the other feeds into the system.

I have last year’s KOP compressor and tank, which each have one port. So how do I connect the pressure relief valve , and the pressure switch? Do I just attach a tee to the compressor with the pressure relief valve on one of the branches? Do I then need a 4-way fitting on the tank to include an inlet, outlet, and pressure switch?

Yes. You will need to put a tee (or perhaps more conveniently a “y” connector depending on space) at the compressor for the relief valve. In addition, you will need to add branches for the manual release valve, switch, tank and regulator input on the high-pressure side, probably with the tees you were talking about. We usually use three tee’s to do this, putting the switch in line with either the tank or manual release.

Or at least 2 “T” fittings.

As long as the pressure relief valve, etc are on the same pneumatic branch as the compressor, and reasonably near (so that some odd failure of the hose, say it getting pinched, won’t cause a safety issue) you should have no troubles.