Bought this for my daughter's Science Olympiad studies in thermodynamics. Gives a real-world application of the first and second laws of thermodynamics in a tight little package. Takes a bit of practice to learn its neuroses, but if you follow the directions then all should be well. Had a bit of grief with the unit after its first run. The piston was sticky, preventing facile motion, and oiling the piston stem didn't seem to help. I wound up disassembling the unit, wiping it down, and applied oil directly to the piston before re-assembling (yes, I voided the warranty). After some heat, steam and motion, it ran like new. A 20ml fill should easily last a half hour. On my unit's latest run, the candle burned down enough that the boiler was slightly underpowered due to the increased distance from the flame to the boiler base. That run went for over an hour on a 15ml fill. Some things I learned along the way: At top speed the engine takes on a "pocketa-pocketa" sound that sounds like metal-on-metal, but it's probably just the high-pressure steam decompressing in the outlet beyond some transition temperature. It should not be a problem, but if it bothers you, raise the boiler a tiny bit by putting shims between the stand and the boiler support. Something like the flat of a toothpick (or three) is enough. It will reduce the speed of the engine slightly, and make it run quieter and probably longer. It is very hard to overpressurize this thing. It has a run pressure of 1atm (gauge) and the unit is factory tested to a burst pressure of 3atm (gauge). Steam will push its way out through the primary borehole long before it gets that bad. Oh, and on that point... Use soft, purified, or ideally distilled, water. Hard water will corrode the interior and clog up that primary borehole, which you don't want to do, since it also doubles as your primary overpressure outlet. I use store-bought bottled water, and it's fine. It takes about 10-15 minutes for the boiler to come up to pressure. Prime the engine by pushing the flywheel forward, as it will almost certainly not start of its own accord. It might spurt a bit of water through the outlet at first, which is just the effect of condensation in the borehole. That's fine, just keep moving the flywheel until the water clears. Once the piston is at temperature, it should run without trouble. It's a fun and instructive little toy, and I'm glad I got it.
