Engineering Wonders of the World
Volume I

RAILWAY BRAKES. 251 the motor of which is thrown in or out of action by the decrease and increase of pres- sure, replaces the steam-pump. Slipping Coaches. Before a coach is slipped from the rear of a train, the taps on each side of the coupling joint of the train pipe must be turned off by the guard in the “ slip,” and the joint be uncoupled. Special reservoirs under the “ slip ” enable the guard to reduce or increase the pressure in the train pipe (according to the system employed) if, after the slip has parted from the train, he finds that he has applied his brakes too hard and desires to release them. DIAGRAM TO SHOW THE PRINCIPLE OF THE JOY VALVE GEAR. This gear, which is used extensively for locomotives on the London and North-Western, North- Eastern, and Lancashire and Yorkshire Railways, includes no eccentrics. Motion is imparted by the connecting rod, through a series of links and levers, to a block which is pushed up and down in a curved pivoted guide held in any desired position by the reversing lever. To the block is attached a radius rod which directly. operates the valve rod. When the guide is tilted, as shown in the diagram, the movements of the block affect the valve rod, as A is nearer the valve chest than is B. To reverse the engine, the guide is tilted over in the opposite direction, and to obtain mid-gear” set vertically. Under the heads of simplicity, efficiency, and lightness, the Joy gear has much to recommend it.