When the cylinder is full, the entry valve is closed and a release valve is opened. The steam then escapes and the resulting vacuum draws the piston back toward the near side of the cylinder. The release valve is then closed and the entry valve opened again. As the steam enters, the piston responds by again moving toward the far side of the cylinder and the process repeats itself. The second type of steam engine is the turbine in which a jet of steam is directed at the blades of a rotating wheel.
Steam engines rely on boilers to store steam at a pressure necessary to operate the engine.
Boilers on steam engines have a safety valve which permits steam to escape when the pressure in the boiler threatens to cause an explosion. It is extremely dangerous to operate a steam engine with a defective safety valve. In the movie, the safety valve on the boiler is defective. The steam engine was first perfected in England in 1769 by James Watt. The invention of the steam engine was a necessary precondition for the industrial revolution.