Steam Engine Stack
Name: Elizabeth T.
Date: August 2004
Is the stack on top of the steam engine called a smoke
stack? If so, where does the steam escape from?
A steam engine will typically consist of a "firebox" or place with
something is burned to produce heat, a boiler which contains the water
to be converted into steam, and a piston/valve arrangement which
converts the steam energy into mechanical motion.
If you imagine a steam powered railroad locomotive, the stack on the top
front of the engine is indeed the smoke stack. This is where the by
products of burning wood or coal exit the firebox. The steam is
released along each side of the engine at the exit ports of the valves
which are parts of the pistons. Of course if the boiler pressure gets
too high, steam can exit out of any number of unintended locations! :-)
By steam engine, I assume that you mean steam locomotive.
Steam locomotives are rather sophisticated inside. The smoke stack is part
of a system that helps pull smoke through the firebox and boiler tubes to
boil the water.
The smoke stack sets on top of the locomotive. Under the smoke stack is a
"draft pipe" that goes a couple of feet into the locomotive. It has a
tapered shape for easy flow of smoke up and out of the smoke stack. In
addition, exhaust steam is used to forcefully blow the smoke out of the
smokestack. The exhaust steam from the cylinders goes into an "exhaust
nozzle" that is underneath the draft pipe, and it shoots upward to draw
smoke along with it. The amount of suction out of the stack is called the
When a locomotive is moving, a mixture of smoke and exhaust steam comes out
of the stack. When a locomotive is stationary, there is no exhaust steam to
help with the draw. In this case, the engineer opens a valve and some extra
steam is blown up through the nozzle to help with the draw to keep the fire
hot. This device is called the "blower."
This is very useful: http://www.sdrm.org/faqs/boilers/
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Update: June 2012