Patent GB-899072-A (GB)
Title: Improvements relating to railway vacuum braking apparatus
Inventor: MARSH GERALD CRANTON
IPC: B60T13/46
Filed: 1958-02-03
Abstract: 899,072. Railway vacuum braking apparatus. GRESHAM & CRAVEN Ltd. Jan. 20, 1959 [Feb. 3, 1958], No. 3427/58. Class 103 (1). A valve arrangement, for railway vehicle vacuum braking apparatus, maintains a communication open whilst the train-pipe vacuum is increasing to, or is constant at or above, a predetermined value and is closed whilst the train-pipe vacuum is constant, or decreasing below that value. The communication 15, between an auxiliary exhauster in a guard's van and the train-pipe 16, comprises two branches 13, 14 containing isolating valve 11 and by-pass valve 12 respectively, the valve 11 including a member 19 biased to the closed position by spring 20 but opened when the predetermined value of vacuum (15 inches of mercury) exists above diaphragm 18, and valve 12 comprising a gravity closed valve member 21 which is opened by a plunger on a diaphragm 22 against spring 23 when the pressure in chamber 24 is a lesser degree of vacuum than the train-pipe vacuum acting above the diaphragm 22, by a predetermined difference (2 inches of mercury). An isolating valve 25 comprises a gravity check valve 27 opened against spring 29 when vacuum above diaphragm 28 is at least equal to the predetermined value and preferably 16 inches of mercury, to connect the train-pipe to the chamber 24 which is also connected to a reservoir 26 maintained at a degree of vacuum less than the train-pipe vacuum by at least the predetermined difference (preferably 3 inches of mercury) by a loaded check valve 31. Before charging, atmospheric pressure throughout the system maintains the valves as shown, but on charging, the main exhauster on the locomotive withdraws air from the train-pipe 16 and valves 11, 12, 25, the ball valve 27 remaining closed and the train-pipe vacuum acting above diaphragm 22 rapidly establishes the predetermined pressure difference across the diaphragm, to open valve member 21 to connect the auxiliary exhauster to the train-pipe to rapidly charge the rear portion of the train. When vacuum reaches the predetermined value (15 inches), valve 11 opens and when it reaches 16 inches the diaphragm 28 rises to open valve 27 to equalise chamber 24 with the train-pipe so that spring 23 closes valve member 21. The control reservoir 26 guards against leakage past valve 27 when pressure equalisation between the train-pipe and chamber 24 is being delayed. On braking and a decrease of vacuum in the train-pipe, the valve 11 is closed by spring 20 and due to the direction of check valve 27, chamber 24 rapidly equalises with the decreasing train-pipe vacuum to maintain valve 21 closed. The auxiliary exhauster is therefore cut-off from the train-pipe except through a restricted port 30 in valve 12 enabling the exhauster to balance external leakage into the train-pipe which could build up and cause brake application. During brake release the valve arrangement acts as during charging, valve 12 initially circumventing valve 11. The valve 25 may be replaced by a check valve permitting flow from the train-pipe which is circumvented by a restricted passage to retard equalisation of chamber 24 with the increasing train-pipe vacuum. Valve 31 is omitted from the apparatus shown in the Provisional Specification.