Patent GB-768112-A (GB)
Title: Improvements relating to vacuum braking apparatus for railway vehicles and the like
IPC: B60T13/46
Filed: 1954-11-22
Abstract: 768,112. Fluid-pressure brakes. WESTING- HOUSE BRAKE & SIGNAL CO., Ltd., and MERRILEES, J. D. Oct. 31, 1955 [Nov. 22, 1954], No. 33687/54. Class 103 (1). In a vacuum braking apparatus of the kind which includes a brake cylinder having an upper chamber normally in communication with the vacuum reservoir and a lower chamber normally in communication with a brake pipe, the chambers being separated by means of a piston or diaphragm ; the thrust on which, due to the difference in pressure in the two chambers, is transmitted to brake shoes on the vehicle, a valve device is provided which functions to limit the maximum braking force which can be obtained to a value depending on the vehicle load. In the embodiment illustrated, the valve device comprises two valve chambers 5, 6 separated by a flexible diaphragm 4 pieced at its centre and formed with a port 7 normally closed by spring-loaded valve 10. Chambers 5 and 6 are in communication with the upper and lower chambers respectively of a vacuum brake cylinder. Secured to the upper face of the diaphragm 4 is a valve housing 8 which carries a stem 18 extending axially upwards through port 16, through chamber 17 which is in permanent connection with the brake pipe, through top cover 19 of casing 1 and extending into sleeve 26 which is connected in a suitable manner to a weighing mechanism such that as the vehicle load is increased, the sleeve moves upwards imparting an increased upward thrust through spring 28 to the stem 18. When the system is initially charged, the brake pipe is evacuated and the chambers 5, 6 and 17 are balanced, the normally seated valve member 10 being seated and a normally unseated valve member 22 being unseated. If air is admitted into the brake pipe in order to cause application of the brakes, air will flow from the brake pipe into chamber 17 through normally open port 16 into chamber 6 and thence to the lower chamber of the brake cylinder. Flow of air into the upper chamber of the brake cylinder is prevented by closed valve member 10 and the brakes are applied. If the admission of air into the brake pipe increases to increase the downward thrust on the diaphragm 4 and overcome the upward thrust on the stem 18 due to the vehicle load, the stem 18 moves downwards and valve member 22 closes to cut off communication between the brake pipe and the lower chamber of the brake cylinder. Should there be any leakage of air into the lower chamber of the brake cylinder caused by the valve member 22 leaking badly, the diaphragm is deflected downwards and unseats the normally seated valve member 10 against projection 12 to establish communication between the upper and lower chambers on the brake cylinder until the difference in pressures in these two chambers is reduced to the magnitude appropriate to the vehicle load. Whereupon the diaphragm is again deflected upwards and the valve member 10 is reseated. The brakes are released by once more evacuating the brake pipe and the brake cylinder as described with reference to the initial charging of the system. A modified construction of the valve is described and illustrated in the Specification wherein the stem 18 and the spring 28 are wholly enclosed in chamber 6.