As far as I know, this is the only propane heated, manually pumped, unicycle towed espresso machine in the world. It was built up for Burning Man and its construction was extensively documented on HomeBarista.com (search pocojoe and playa espresso cart). I've moved on and now this project needs a new wrench to put it on the back of a bike and go in search of fun. The machine is based on a two group La San Marco Leva (not lever) - a truly mechanical group control so no solenoid is required. The burner assembly is double safety - a pilot light thermocouple controlling a millivolt propane control valve, with pressostat control of pressure. The base has room for "suitcase" water and waste water, and there is a manually cranked Pharos grinder to get the crowd involved.
For someone who wants to learn about espresso and go guerilla in serving it, taking the cart to where ever a bike can go, this is the place to start.