A steam generator is a piece of equipment designed to convert a liquid, which is usually water, into a vapor, referred to as steam. The liquid is heated by the burning of some sort of fuel, such as wood, coal, petroleum or natural gas. The change from a liquid to a vapor creates pressure and then expansion, which can be channeled and directed as an energy source. Steam-powered pistons were instrumental in the growth of early factories, railway locomotives, steamships and many other examples of mechanical equipment.
One of the earliest uses of the steam generator was in the steam locomotive. Fuel, in the form of wood or coal, was fed into the firebox. The resulting heat was channeled through a system of tubes, which heated the water that was stored in a special holding tank. After the temperature reached the boiling level, the energy created from the steam then drove the pistons, which turned the wheels on the engine. The primary purpose for the steam was to propel the train, but it also had other uses, including powering the brakes and the whistle.
Employing the steam generator to power locomotives was a great improvement in transportation in the early 17th century, but it did have its drawbacks. They were accompanied by a great deal of smoke, and there was always the possibility of fires resulting from sparks and burning cinders. In addition, the tank holding the water had to be closely monitored to make sure that the water remained at a certain level. Allowing the tank to run out of water was extremely dangerous, because it could result in a fire or an explosion.
Even after the fire boxes were removed and diesel became the power source, steam generators were still used on trains. Some of the surplus steam from the original steam locomotive had been routed to the passenger cars to heat the interior and keep the occupants comfortable. When that method was no longer available, special steam generators were added specifically for the purpose of heating the cars. Today, most trains in operation around the world are heated by an electrical system.
A steam generator is also sometimes referred to as a boiler. The classification of the different types of boilers is generally based on configuration. For example, the Haycock or pot boiler is shaped like a kettle, and the fire-tube boiler is designed in the shape of a barrel with a connecting tube-like structure.