Page:Motors and motor-driving (1902).djvu/149

Rh of the float  actuates two arms  which are attached to the float spindle, and which depresses this float spindle until the conical end of it blocks up the aperture through which the petrol ascends. No more petrol can thus reach the float chamber until, by the depression of the float, this valve spindle is allowed to rise. By this means the petrol is always kept at a constant level in the float chamber. At there is a tap fitted by means of which a further supply of air can be admitted to the carburetter to suit the condition of the atmosphere or the varying demands of tube or electric ignition. By screwing home into the socket  the supply of petrol is wholly stopped. There are many varieties of the spray carburetter, such, for example, as the well-known Longuemare and the carburetter used on the De Dion car (as distinguished from the De Dion cycle), but in all the general principle is the same. In most of them a hand-worked lever regulates the quality of the mixture.

Two systems of feeding the spray carburetter are used, known respectively as pressure and gravity. In the case of the first named, the petrol tank is situated in the body of the frame at a lower level than the carburetter. Air is pumped into this tank, the pressure afterwards being kept up by the exhaust gases. The pressure of this air on the surface of the petrol forces it upward through a pipe into the carburetter, and where tube ignition is used, into the burners.

With the gravity-fed carburetter the tank is fitted in the body of the car, either under the front seat, between the front and back seats, or under the bonnet at a higher level than the carburetter, and the petrol finds its way into the carburetter by force of gravity.

Both systems have their adherents, but gravity is rapidly ousting pressure. The former certainly can be claimed to be the most simple and effective, but the latter is perhaps the safest, because any leakage of petrol can immediately be stopped by turning off the pressure cock.