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Name: Elizabeth T.
Status: Educator
Age: 60s
Location: N/A
Country: N/A
Date: August 2004


Question:
Is the stack on top of the steam engine called a smoke stack? If so, where does the steam escape from?



Replies:
Elizabeth,

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! :-)

Bob Hartwell


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 "draw."

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/

Bob Erck



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