. Electric railway journal . he distinguish-ing characteristic of straight-air equipment is that thebrake can only be applied by conscious manipulation bythe operator. If, however, the brake is automatically because of the slower rate at which reservoir air flowsby the feed groove into the pipe, a pressure differen-tial is built up upon the piston, which forces it andits attached slide valve away from the reservoir. Thismovement connects the slide-valve ports in a differentway from that existing in release position and therebycauses the brakes to apply. From this explanation it is evident that
. Electric railway journal . he distinguish-ing characteristic of straight-air equipment is that thebrake can only be applied by conscious manipulation bythe operator. If, however, the brake is automatically because of the slower rate at which reservoir air flowsby the feed groove into the pipe, a pressure differen-tial is built up upon the piston, which forces it andits attached slide valve away from the reservoir. Thismovement connects the slide-valve ports in a differentway from that existing in release position and therebycauses the brakes to apply. From this explanation it is evident that when thepressure in the pipe is reduced with sufficient rapiditythe brakes will apply, whether or not this be broughtabout by the operator. That is, the brakes apply auto-matically whenever a rapid reduction of pressure in thepipe is obtained. If both service and emergencyapplication are brought about by reductions in pipepressure the equipment is said to be automatic brakeequipment. If, however, only the emergency applica-. SAFETY CAR CROSSING DRAWBRIDGE IN TAMPA applied under certain conditions, independent of theoperator, then the equipment becomes an automaticequipment. For an automatic brake the triple-valveprinciple is employed. A triple valve is a device in which a piston operatesin a bushed cylinder. To the stem of the piston isattached a slide valve which travels back and forthover a flat slide-valve seat, covering and uncoveringvarious ports in its movements. The slide-valve sideof the piston is connected to a reservoir. The otherside of the piston is connected to a pipe leading to asource of air supply. When air is admitted to thispipe the pressure built up on the pipe side of the triplevalve piston forces the piston to move toward the reser-voir until it encounters a stop. This position is knownas release, and in release position the reservoir andpipe are connected by a small feed groove in the pistonbush. Consequently air flows by the feed groove andeventually pip
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