coils by the water pump. At the same time the greater supply of water requires a larger supply of oil to the burner to keep the coils hot enough to evaporate it, and the stroke or up-and-down motion of the lever l can be varied by shifting the shaft
_0294a.jpg)
Fig. 13.—The Serpollet Water and Oil Pump
a sideways, so that cams of varying degrees of eccentricity can be brought under the roller r, and its motion increased or decreased as required. As the two pumps are both connected to the lever l, it will be seen that whether they are giving full
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Fig. 13a.—Example of Cams of Different Throws
supply or anything below it the proportion of six parts of water to one of oil will always be maintained. On some Serpollet cars the pumps are horizontal instead of vertical, but they operate in a precisely similar manner.
Fig. 13a shows three cams in a row. These cams are eccentric discs fixed on a revolving shaft, and as the faces of Nos. 2 and 3 do not project so far from the shaft as 1, if the roller r be introduced against the face of 3, for instance, it will be moved up and down less than if it were bearing against the
