. Scientific American Volume 10 Number 24 (June 1864). n-structor the Diaphragm Pressure Wheel, for it actsby impact, or the dead weight and velocity of thecurrent in the race, in the same general way thatsteam pushes on the piston of a steam engine. Theconstruction and operation will be understood by re- Expansion Gear on Locomotives. The history of variable expansive gear will proveinteresting. It is uncertain when lap was first ap-plied to the slide valve with a view to expansiveworking. Yet it is nevertheless certain that lap wasoften given to steam engine valves long before even1830. In t
. Scientific American Volume 10 Number 24 (June 1864). n-structor the Diaphragm Pressure Wheel, for it actsby impact, or the dead weight and velocity of thecurrent in the race, in the same general way thatsteam pushes on the piston of a steam engine. Theconstruction and operation will be understood by re- Expansion Gear on Locomotives. The history of variable expansive gear will proveinteresting. It is uncertain when lap was first ap-plied to the slide valve with a view to expansiveworking. Yet it is nevertheless certain that lap wasoften given to steam engine valves long before even1830. In the French patents are many drawings ofvery early engines, in which the valves were movedby cams, and which had a lap at each end equal tothe width of the steam ports. It is true that thecams were made to move the valves quickly, buteven then some time was necessarily occupied in thetraverse of the valve through the sum of the lap atboth ends, and during this time the steam already inthe cylinder must have been expanding. All the pa- t L-.;| f z : HZj. I SMITHS WATER PRESSURE WHEEL. ferring to the following description:—The shaft, A,has four arms, B, which are forked at the ends andcarry idler pulleys, 0. These pulleys bear on a rub-ber diaphragm, E, which is attached to the case, is also a scroll or case, G, having four or moreinlet passages, H. The operation is as follows:—when the water enters the scroll it passes around tothe openings just mentioned and strikes the innerface of the diaphragm, against which the pulley isresting, as in Fig. 2; this pulley is thereby forcedaround, and as each one in turn passes the waterpassage, an impulse is given which keeps up the firstmovement transmitted, and the machinery continuesin motion; the water is then discharged from the caseof the diaphragm through openings at the bottom,which are not shown. In some instances valves areplaced in the inlet passages as shown at I; by meansof these the water can be shut off at any point;
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