screwed up to the petrol pipes so that the petrol passes through it to vaporise it before it is admitted to the burner. The burner is then lighted, and as soon as the boiler becomes hot enough to vaporise the petrol, which, it will be remembered, is passed through it, the firing iron, as the U tube is called, can be disconnected. This arrangement can now be dispensed with, and in place of it a small Bunsen burner is placed at the side of the fire-box, playing on a coiled tube, through which the petrol passes on its way to the burner. When this coil is heated the small starting burner, which is on a hinge, is turned away from it, but acts as a pilot light, so that the main burner can be almost turned out when stopping or running down hill.
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Fig. 4.—Automatic Fire Regulator
The Automatic Fire Regulator.—Many steam vehicles are fitted with an automatic fire regulator, of which the Kelly fitted to the Milwaukee is taken as an example, and it is the same in principle as most others. Fig. 4 is a section of the device. A diaphragm or circular plate is pressed by the steam from the boiler, and as the pressure rises the diaphragm is, so to speak, bulged. In its turn it pushes the plunger rod, which has a conical head a, forward, so that it closes or partially closes the end of the tube b, through which the vapour passes into the tube c on the way to the burner. When there is no pressure in the boiler the coil spring round the plunger rod holds it back, so that the orifice closed by a is fully opened and the vapour passes freely into c and on to the burner. As steam pressure rises the diaphragm is gradually bulged, so that a
