DETAILS OP SCREW ENGINES.

297

when the steam power is disabled or notavailable. This example has been fitted withthe engines, 700 horse power collectively, inthe Mail Transport S.S. “ Jumna.”

Direct acting steam starting gear has beenadopted by Messrs. Napier, and the applicationwill be readily understood by referring toPlate 18, where the steam cylinder is directlyabove the lever in connection with the weighshaft. This arrangement dispenses with spurgearing, therefore the area of the cylinder isdirectly proportioned to the power. The avail-able pressure of steam is, however, the principalcause to be considered in the matter.

Other firms have adopted the type of gearnow alluded to, and the practice of Messrs.Pavenliill is worthy of notice. Their ideas on

Fig. 152.

messes, eavenhill’s steam starting gear.

the subject will be understood by the Fig. 152,h e ing a plan and elevation of a pair of cylin-ders side by side, the piston rods of both being

connected directly to the levers on the weighshaft. The slide valves are manipulated fromthe platform, also the steam cock, situatedbetween the levers for working the valve rods.

EXPANSION VALVES AND GEAR.

The effect of using steam expansively istreated at some length from page 212 to page216, inclusive; it is therefore sufficient, as apreface to the present subject, to state that thesteam is intercepted between the boilers andthe slide valve, by the different modes now tobe described.

If simplicity of arrangement is an achieve-ment, Messrs. Penn can claim high honoursfor their production, shown by Fig. 153—page 298. The expansion valve is the grid-iron type, sliding on a seating of correspondingform: both being shown in section and plan,further allusion is scarcely requisite. Withreference to the gear, it consists of an eccen-tric as a prime mover, and the rod is formedwith a slot and lift gab at the other extremity.The pin is fixed to a sliding block, which iscontained in the grooved portion or link,supported by the bracket at the front of thecasing. The cranked handle, above the pro-jection over the groove, is fixed on the screwpassing through the block; thus the eccentricpin can be shifted in the groove at pleasure, orto suit the grade of expansion settled on.Suitable means for disengaging the rod andretaining it out of gear is insured by the loop,guide rod, and hand lever, shown above thebracket. The valve rod is connected by flatbars and pins to the link, and guides areobviated by the sufficient strength of the rodand shortness of the stroke.

2 u