A steam engine is a machine that burns coal to release the
heat energy it contains, so it is an example of what we call
a heat engine. It is a bit like a giant kettle sitting on top of a
coal fire. The heat from the fire boils the water in the kettle
and turns it into steam. But instead of blowing off uselessly
into the air, like the steam from a kettle, the steam is captured
and used to power a machine. Let's find out how!
What is a steam engine?
They were first invented by Thomas Newcomen in 1705,
and James Watt (who we remember each time we talk
about "60 - watt light bulbs" and the such) made big
improvements to steam engines in 1769. Steam engines
powered all early locomotives, steam boats and factories.
Steam engines were the first engine type
to see widespread use.
The high-pressure steam for a steam engine comes from a
boiler. The boiler's job is to apply heat to water to create
steam. There are two approaches: fire tube and water tube.
A fire-tube boiler was more common in the 1800s.
It consists of a tank of water perforated with pipes. The hot
gases from a coal or wood fire run through the pipes to
heat the water in the tank, as shown below:
In a fire-tube boiler, the entire tank is under pressure, so if
the tank bursts it creates a major explosion.
Boilers
It explains where the "choo-choo" sound comes from.
The following diagram shows the major components of a
piston steam engine. This sort of engine would be typical
in a steam locomotive.
The engine shown is a double-acting steam engine because
the valve allows high-pressure steam to act alternately on
both faces of the piston. The following diagram shows the
engine in action.
You can see that the slide valve is in charge of letting the
high-pressure steam into either side of the cylinder. The
control rod for the valve is usually hooked into a linkage
attached to the cross-head, so that the motion of the
cross-head slides the valve as well. (On a steam locomotive,
this linkage also allows the engineer to put the train into
reverse.)
You can see in this diagram that the exhaust steam
simply vents out into the air. This fact explains two
things about steam locomotives: It explains why
they have to take on water at the station -- the water
is constantly being lost through the steam exhaust.
Steam Engine Operation
The two large tubes at the top of
the boiler are the main steam pipes
which collect steam from the dome
and transfer it to the steam chest
and cylinders.
The firebox is surrounded by a water jacket. Inside the
boiler there are smoke tubes which heat the water and
convey the hot exhaust to the smoke box where the
gases are drawn out through the chimney. The picture is
of a locomotive boiler, the smoke box has been removed
and you can see where the smoke tubes are positioned.
The two essential ingredients to make a steam engine
work are fire and water. The fire is created in the firebox
using coal, this in turn produces heat which transfers to
the water to produce steam.
7
5
firebox
chimney
boiler
steam dome
coal
wheel
connecting rod
piston cylinder
6
4
1
8
funded by
2
3
Write the appropriate number in
the box to match the word to
the part on the locomotive