This is a vertical single acting steam engine.
It has one cilinder and its run it's very shor: 20 mm.
In this way the engine can work at very high speed. According to my speedometer it work at a maximum speed of 1500 rpm at 4 Atm.
In my brickshelf folder you can find a video of the GY-5 SE in action.
These Air engines are Amazing, just start off with that. But i do have a question for you;
I was just wondering if you could post an image of what the actual piston looks like, with the shaft attached. I'm Building an MLCad Model (www.Ldraw.org) of this engine, and then a working one for a science project. Anyhow, this things sweet. no question about it.