GB751578A - Improvements relating to foot valves for fluid pressure braking systems - Google Patents

Abstract

751,578. Fluid-pressure brakes. WESTING- HOUSE BRAKE & SIGNAL CO., Ltd. Sept. 10, 1954 [Sept. 23, 1953], No. 26281/54. Class 103 (1). In a foot valve for fluid pressure braking systems of the kind which is suitable for controlling in one control operation the independent braking of two separate parts of a single vehicle, e.g. the rear wheels and the front wheels, the valve consists of a fixed main body 1 and an auxiliary body 5 movable within the main body, a first braking circuit being controlled in accordance with the position of a foot-operable pedal by means situated in the auxiliary body and a second braking circuit, independent of the first, being controlled by means situated in the end of the main body in accordance with the displacement of the auxiliary body. The first braking circuit I, e.g. to the front axle circuit, comprises a conduit 11 through which compressed air is supplied from a reservoir into chamber 8 in the auxiliary body 5 and thence through passage 27 in partition 10 via valve 29 to the chamber 9 and thence, if valve 28 is closed by piston 21, via conduit 13 to the brake cylinder. The second braking circuit II, e.g. to the rear axle circuit, is similar to the one described above, i.e. compressed air is supplied via conduit 36 into lower chamber 33 in main body 1 and via passage 41 in partition 35, when valve 43 is open, into upper chamber 34 and thence, if valve 42 is closed by piston 7, via conduit 37 linked to the second braking circuit. In the inoperative position illustrated, valves 29 and 43 are closed and chambers 9 and 34 are open to atmosphere as pistons 21 and 7 are raised off the valves 29 and 43 by springs. When the brake operating pedal 16 is depressed, the piston 18 is depressed and through spring 22 brings pressure to bear on piston 21 until seat 32 makes contact with upper valve 28; thus closing communication between the lower part of chamber 9 and thus the conduit 13 leading to the brake cylinder and atmosphere. Further movement of the piston 21 lifts valve 29 from its seat allowing compressed air to flow from the reservoir via conduit 11 and into the lower part of chamber 9 and conduit 13. With gradual rise of pressure in the lower part of chamber 9, the piston 21 rises against the force of the spring 22 until the valve 29 closes again and interrupts the admission of air into chamber 9 ; the valve 28 being held closed by piston 21 preventing communication between the lower part of chamber 9 and atmosphere. Should the pressure on the lower part of chamber 9 be greater than the effort exerted by the driver, the piston 21 will rise to uncover valve 28 and allow the excess air to escape until equilibrium is restored. The air pressure prevailing in the lower part of chamber 9 at the moment of braking bears on partition 10 of the auxiliary body 5 at the same time as on piston 21, thus causing downward displacement of the auxiliary body 5 and consequently of the piston 7 such that the lower part of piston 7 acts on valves 42, 43 in a similar manner to that described with reference to valves 28, 29. Flutes 21a, 7a are provided on pistons 21, 7 which bear on partitions 10, 35 respectively should there be a break in either of the braking circuits I or II so that effective control of the other braking circuit is provided.