How the steam engine works.
The typical steam engine has a steel fire-tube boiler that contains pressurized water and steam. A firebox is normally located in the rear of the boiler and a chimney or smoke stack in front.
Photo of the firebox from a 1914 wood-burning baldwin locomotive.
The firebox has a water filled steel chamber surrounding the top and sides of the flame in the firebox. A steam engine can burn wood; coal or oil in the firebox.
The fire in the firebox is built on a set of grates where ashes may be separated from the burning fuel. These ashes must periodically be removed from the engine.
If wood or coals are the fuel used in the firebox there is a door at the rear of the firebox that is opened to add more fuel. If oil is used their nearly always is a door for adjusting the air flow, maintenance or for cleaning the oil jets.
To extract even more heat, the smoke and hot air from the combustibles in the firebox travel horizontally through a bundle of parallel tubes submerged in the water in the boiler from the front of the firebox to the front of the boiler.
The heat extracted in the firebox and tubes in the boiler converts the water to pressurized steam in the boiler. To minimize heat loss from the boiler it is normally surrounded with layers of insulation.
The water and steam in the boiler are kept pressurized to raise the boiling temperature of the water and generate high pressure steam. The amount of pressure in the boiler is monitored by the engineer or fireman by a gauge mounted in the cab.
Excess steam pressure can be released manually or can be released though a safety valve. Too much pressure may cause the boiler to burst potentially killing the crew as well as disabling the engine.
At the front of the boiler is the smoke stack or chimney, where steam is ejected drawing the smoke and hot air through the fire tubes in the boiler and out the top of the chimney.
The combustion in a typical steam engine is not very complete leading to a lot of smoke and often sparks being produced. This made these engines very dirty to live around as well as being an acute hazard while passing through a forest, tunnel or snow shed.
The steam generated in the boiler is used to drive the locomotive and also for other purposes whistles, brakes, pumps, air flow, etc.
This constant use of steam requires the boiler to have water continually pumped usually automatically into it. The water is an unpressurized tank, which is periodically topped up at water stops.
The water level is normally monitored with a transparent tube or gauge. If the boiler runs out of water the fire may melt a hole in it, possibly causing an explosion.
In a wreck or accident the boiler may burst, potentially hurting or killing the crew. Start up on a large engine may take an hour or more of preliminary heating of the water in the boiler before it is ready to go.
These are several of the serious disadvantages of steam engines, which have led to their eventual replacement by safer and cleaner engines requiring less maintenance.
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