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The exhaust pipe from the engine which conducts off the exhaust gases after they have done their work in the cylinder is connected to a peculiarly constructed chamber, called a Silencer, attached to the frame of the car. The object of the silencer is to deaden the noise of the escaping gases by:

1. Breaking up the body of gas into a number of fine streams.

2. Allowing the gases to expand and cool.

3. Checking the velocity without putting back pressure on the engine.

4. Reducing the pressure of the gases till they are as nearly as possible the same as the atmosphere. To do this, the chamber is divided up into a series of compartments, and the gases in their passage from one to the other have to pass through baffle plates drilled with a number of fine holes, the combined area of which must be considerably in excess of the area of the exhaust pipe, to allow of a free passage for the expanding gases. The flow is thus broken up and subdivided into a number of fine streams of cool gas at or near atmospheric pressure, which cause little or no noise on their escape into the air. It is the sudden expansion of the gases at a high pressure which causes the noise.

Figs. 12 and 13 depict two types of silencer which are very largely used. Fig. 12 shows a sectional view of a silencer composed of three concentric cylinders,, , and. is composed of a tube or inverted cylinder of sheet steel; is the second tube similarly constructed; while  is an extension of the exhaust pipe from the engine. Two chambers, and, are thus formed. The exhaust gases from the engine enter, and passing through a number of holes at the end of the pipe at , expand in the chamber. Passing from the chamber through the holes at, the gases enter the chamber , where a further expansion takes place. Finally the exhaust is ejected