Page:Motors and motor-driving (1902).djvu/143

Rh is very simple. When the cam revolves so that the projecting part comes on top, it pushes up the plunger. in turn pushes the spindle, which carries on its top the exhaust valve , and the latter is consequently removed off its seating, and permits the exhaust gases to escape. As continues to revolve  the protruding portion sinks from under, and the spring  pushes the exhaust valve  to its position on its seating. Needless to say, the gear wheels and  must be so set that the cam  will open the exhaust valve  at exactly the right moment.

The action of the exhaust valves in the two cylinder engines of the Daimler type is described further on under the heading Governors. The principle is exactly the same.

The mixture, the ignition of which causes the impulse which drives the engine, is formed from the vapour which rises from petrol or motor-car spirit when mixed in proper proportions with air in other words, when this air is carburetted. The chamber in which this mixing takes place is consequently called the carburetter. There are three types of carburetter, which we will now describe.

(1) The Surface Carburetter, as used on the De Dion Motor Cycle. This carburetter is so designed as to give a considerable surface of spirit, off which the vapour rises, and together with a certain quantity of air is sucked into the mixing chamber, which is commonly known as the twin tap. In this mixing chamber the proper proportions of air and gas are finally regulated so as to give a perfect mixture. Fig. 7 explains the construction of the carburetter.

is a pipe taken off the exhaust which carries a portion of