GB250846A - Improvements in pneumatic braking apparatus for railway vehicles - Google Patents

Abstract

250,846. Howe, W. K. April 6, 1925. Fluid-pressure. - The manually-operated driver's valve of a fluid-pressure brake is adapted also to be operated automatically to apply the brakes, the arrangement being, such that when an automatic brake application is initiated, it cannot be prevented by the driver, but may be converted by him into an emergency application. Rotatably mounted on the valve stem 38 which operates the usual rotary valve, 36 of the driver's valve is a gear sector 45 which is engaged by a rack 46 attached to a piston 49 working in a cylinder 31 and normally held in the position shown in Fig. 1 by a spring 50. On the valve stem 38 is also mounted, slidably but non-rotatably, a collar C provided with a lug 53 adapted to be engaged by the edge of the sector 45 when the latter is rotated in an anticlockwise direction; a lug 64 adapted to be engaged by a pin 63 when a stem 60 carrying the brake handle 71 is rotated in an anticlockwise direction: and a lug 67 to which one end of a coiled spring 65 is connected, the other end of the spring being attached to the stem 60. The valve 36 can thus be moved positively to application position either by the sector 45 or by the handle 71, but can be restored to release position only by the action of the spring 65. The supply of pressure fluid to the cylinder 31 is controlled by an electrically-operated valve E.P.V., which, with the solenoid 84 energized, is held in the position shown, to connect the cylinder to atmosphere at 89 through a valve 86, but drops, when the solenoid is de-energised, to close the valve 86, and open the valve 85 to connect the cylinder to the main reservoir at 87. The piston 49 is then moved to the left and the sector 45 operates the collar C to move the valve 36 to application position. If the handle 71 is free, it will partake of this movement under the action of the spring 65, but if it be held by the driver or be moved towards release position, the movement will take place against the action of the spring, which merely becomes further tensioned. When the valve 36 has been moved to service position. the movement of the rack is arrested by its contact with the valve casing. The driver can then manually operate the valve 36 to emergency position if necessary. When the coil 84 is again energized and the cylinder 31 vented, the spring 50 will return the rack 46 and sector 45 to normal position, but the valve 36 remains stationary, and the driver can then release the brakes normally, the spring 65 being sufficiently tensioned to move the valve 36 when the opposing pressure of the sector 45 has been removed. The control of the valve E.P.V. may be effected by an electropneumatic valve controlled by means partly on the track, and a contact segment is provided on the collar C, adapted, when the latter is in application position to close an acknowledging circuit which then prevents actuation of the control devices governing the operation of the valve E.P.V.