Little Engine Display
Once you've spent all this time building these engines, there's no use hiding them in a closet. We use a semi-permanent display on a rolling cart. The engines are bolted to the cart. We've made a manifold (upper right side of photo) with a quick couple connector and numerous small air supply hoses (that go to each engine). Since we didn't feel like spending the money on 8 or 9 air regulators (each engine has different air pressure needs), we made "pinch tabs" (bottom sketch) that squeeze each hose down with 8-32 screws. The screws are turned to adjust the air supply (it's crude, but it's works......and it's cheap). We set the engines up so that they run as slowly as possible......it's easier to see the mechanical action that way.
Normally, we leave it hooked up by our lab door (which is adjacent to a main hall in our school). If we get school visitors or have an open house, we turn it on......always draws a big crowd. Occasionally we bring it to other non-school venues, but without compressed air (to run it), it's not as interesting.
Wal-Mart sells a small 110 volt compressor with tank for $99. We're thinking of buying one and mounting it on the cart......then we can display the engines (running) at places without a compressed air supply.