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122 most general use. The Daimler form is perhaps the most typical, and consequently we will proceed to describe it by means of diagrams. Briefly put, it consists in temporarily preventing one or more exhaust valves from opening, and consequently for the time being a fresh charge cannot be admitted into the combustion chamber, as the latter is charged to its fullest capacity with the exhaust gases. As already explained, the ordinary exhaust valve is opened by means of a plunger actuated by a cam on the two-to-one shaft (see fig. 6).

Figs. 14 and 15 show a side view of the mechanism which operates the Daimler exhaust valve. Taking fig. 14 first:— corresponds to the stem of the exhaust valve marked in fig. 6, while the shoulder  is the plunger, which, acting upwards, pushes the valve open and so allows the exhaust gases to escape. is a roller free to revolve on the spindle 2. is the two-to-one shaft marked in fig. 6, and  is the cam on this shaft corresponding to cam  in fig. 6. It is shown in dotted lines because it is not visible when looked at from this aspect. It will be seen, however, on shaft in fig. 15.

Now, as shown in the illustration, the exhaust valve is closed, but when the cam revolves another half-turn, the projection on it bears against roller, and so pushes upwards the arm , which is hinged on the spindle. Needless to say, the shoulder is thereby raised, and in turn pushes upwards the lifting rod or digger, thus opening the exhaust valve.

We will now turn to fig. 15. This shows how the various systems of levers in fig. 14 operate so as to prevent one or more of the exhaust valves from opening, and so make the engine cut out on one or more cylinders by preventing the ingress of a fresh charge of mixture to the combustion chamber. It will be seen that the eccentric portion of the cam, is now uppermost, and is bearing against the roller , so as to elevate the arm with its shoulder. In fig. 14 the end of the spindle, which is commonly known as the digger, rests on shoulder , but in fig. 15 it will be observed that has been pushed outward by the arm , so that the point of the digger