The vacuum machine (vacuum engine) is an external combustion engine and works as follows: The flame produced by the container with alcohol is absorbed into the cylinder by a small hole and is trapped with a valve. The air inside the cylinder is now warm and swells, with the result that pushes the piston. After the motion of the piston in the cylinder air cooled, and creates a pressure drop that absorbs piston again. So the valve opens again and repeats the cycle of motion.