io8

MODERN STEAM PRACTICE.

on at the top, fitted with sliding blocks. .There is a weigh-shaft,working in suitable bearings, placed on the cylinder. This shaftsometimes curves round the cylinder, with a bearing for each end,

but the general plan is to forgein one piece the levers for takingthe valve rod and quadrant, in-troducing a long bearing betweenthem, oscillating on a single jour-nal fitted to the cylinder. Bothends of the levers for taking thequadrant and valve spindle arefitted with pins and loose slidingblocks. Where but one valve isfitted, the centre of the pin in thelever for the sector end is placedon the centre line of the engine.When the valve is at half stroke,the levers being at right anglesto the centre line of the valvespindle, the distance from thecentre of the pin to the centreline of the trunnion for the cylin-der is the radius of the link orsector. Two valves are, how-A A ' Sector sIide b, : c t„ tric B ; 0 P r f ° r the Sab “ d ° f ever, generally adopted, necessi-

tating the blocks for the sectorbeing kept slightly apart; then the radius for the sector is measuredfrom the centre of one of the pins to the centre of the trunnion.Thus it is evident that the arc of the sector must sweep the centresof both pins on the levers, however far distant from each other theymay be placed.

The hand-gear for small power is simply a lever, with link attach-ment to the sector, but for heavy engines a hand-wheel and pinion,working in a rack connected to the sector, is usually adopted;while other arrangements have double eccentrics and link motion,with suitable pin and block fitted to the sector, at a convenient placeas near to the centre of the sector as practicable. The valve leversin connection with the quadrant being placed at the half travel ofthe valve, the vertical distance from the centre of the guide-blockpin on the quadrant to the centre of the main shaft is the radius of

T-ncntvüjn\j Centre-

Fig. 57.—Valve Motion for Oscillating Engines.