Lesson 3
Some military wheeled vehicles use exhaust manifolds with water jackets. The liquid coolant used to cool
the engine passes through the exhaust manifold water jackets before returning to the radiator. This aids in
reducing the temperature of the exhaust gases, reducing the amount of noise, and reducing the damage that
exhaust heat causes to the exhaust system and other nearby parts.
Exhaust passages inside the manifold must be fairly smooth and free of any obstructions that would slow the
flow of exhaust gases.
EXHAUST PIPE
The exhaust pipe is the passageway for the exhaust gases to flow from the manifold to the muffler. It is a
heavy steel tube, usually flanged at both ends, and attached to the muffler.
The diameter of the exhaust pipe is usually determined by the size of the engine. On a small, one-cylinder
engine, a pipe no larger than a household water pipe is enough to do the job. Larger engines may require
exhaust pipes 3 inches or more in diameter to carry the larger amount of exhaust gases.
The length of the exhaust pipe is determined by the design of the vehicle. If the engine is in the front of
the vehicle and the muffler is mounted in the rear, the pipe will be long. (Often, long pipes will be made in
two sections.)
To provide as much road clearance as possible, pipes are formed in odd shapes that fit well up under the
vehicles without touching other components. Pipes are supported from the vehicle frame by hangers. (The
center portion of the hanger can be made of flexible material to absorb vibration.)
MUFFLER
The purpose of the muffler is to muffle the exhaust noise. A "perfect" muffler would silence all the noise
made by the exhaust gases and would eliminate all back pressure. However, it is not practical to make a
muffler so perfect. All mufflers in common use do cause some back pressure and do not silence all the
noise.
There are two basic muffler designs: straight-through and baffle.
The straight-through type has a pipe extending straight through the muffler and a chamber surrounding it.
Holes are drilled all around the pipe, and metal shavings or glass wool is packed in the chamber that
surrounds the through pipe.
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