Patent GB-1204025-A (GB)
Title: Relay emergency valve
IPC: B60T13/40
Filed: 1968-11-08
Abstract: 1,204,025. Brake emergency valves. BENDIX-WESTINGHOUSE AUTOMOTIVE AIR BRAKE CO. 8 Nov., 1968 [13 Nov., 1967], No. 53068/68. Heading F2F. A relay emergency valve for controlling the application of pressure from an emergency fluid pressure reservoir to brake chambers in response to loss of pressure from an emergency line comprises the following features: a casing 14, an emergency cavity 97 for connection to an emergency line 6, an emergency piston 76 in the casing having a motive area exposed at all times to the pressure in the emergency cavity, delivery and exhaust passages 82 and 87 respectively through the piston for connecting the brake chambers to the emergency reservoir and to atmosphere, spring means 74 urging the piston at all times towards a first position in the casing, the piston being movable to a second position in opposition to the spring means in response to pressure in the emergency cavity above a predetermined value, delivery and exhaust valve means 90, 96 and 90, 47 respectively, cooperating with the respective passages in the piston to disconnect the brake chambers from atmosphere and connect the chambers to the emergency reservoir when the piston is in its first position (as shown) and vice versa when the piston is in its second position, the piston being moved from its second position towards its first position by the spring means to effect an emergency application of the brakes in response to decrease of pressure in the emergency line and in the emergency cavity below a predetermined value. As shown, the valve 14 is illustrated in connection with a tractor-trailer braking system which includes a tractor-carried main fluid pressure service reservoir 2 supplied by a compressor (not shown). The service reservoir 2 has leading therefrom an emergency line 6 and a service line 4, the service line passing through a driver-operated brake valve 8 and including a branch leading rearwardly for connection to the trailer system. The "emergency" reservoir 12 is mounted on the trailer and supplies the trailer brake chambers 10 both normally and in emergency. In operation, as the service reservoir 2 becomes charged by the compressor, pressure fluid flows along the emergency line 6 through an emergency port 20, past a check valve 22, through a port 23 and a passage 24 and finally through a port 25 into the "emergency" reservoir 12 until check valve 22 closes. Then pressure fluid passes through a passage 66 into an emergency cavity 97 defined by a shoulder 40 under a fixed intermediate part 17, a shoulder 78 on an emergency piston 76, and 0-rings 98 and 100. The piston 76 is thereby forced down against the action of a spring 74 until a delivery valve seat 96 provided on the piston makes contact with a combined delivery and exhaust valve member 90. Further downward movement of the emergency piston 76 serves to force downwards the valve member 90 against the action of its spring 89, thereby moving the valve member away from an exhaust valve seat 47 provided on a member 46 adjustably screwed into a projection 45 on a relay piston 30. The emergency piston 76 is now held against a shoulder 108. The trailer brake chambers 10 are now in communication with the atmosphere through a delivery port 43, delivery cavity 42, delivery passage 77, the space now provided between seat 47 and valve 90, an exhaust passage 87, and an exhaust port 68 covered by a dust cover 70. When the driver's valve 8 is actuated, pressure fluid passes along line 4 and through a service port 26 into the relay cylinder 28 above the relay piston 26, pressing the piston down against its return spring 38. At a certain stage the exhaust valve seat 47 on projection 46 makes contact with valve 90, thus shutting off the connection between trailer brake chambers 10 and atmosphere, and thereafter the valve member 90 is forced down against its spring 89 by the relay piston 30 until seat 96 is uncovered. When this occurs, pressure fluid is enabled to pass from the "emergency" reservoir 12 through port 25, into passage 24, through permanentlyopen ports 84 in emergency piston 76, into a delivery chamber or passage 82 therein, along flutes 90, through the space now provided between valve 90 and seat 96, along delivery passage 77 into delivery cavity 42 and through delivery port 43 to the trailer brake chambers 10 to apply the brakes. When the driver's valve is released, the relay piston 30 returns to the position shown in the Figure, but the emergency piston, it will be recalled, is still held in contact with shoulder 108 by pressure in cavity 97, and the exhaust aspect of the valve assembly is open. Upon sudden rupture of the emergency line 6, pressure fluid escapes from cavity 97, whereupon spring 74 raises the emergency piston 76 (within which valve 90 is being held against seat 96 by its spring 89), until valve 90 is stopped by seat 47 (thereby cutting off the brake chambers from exhaust). Thereafter, piston 76 rises further until seat 96 leaves valve 90, and further still to the rest position shown in the Figure, where the trailer brakes are on. In the event of a alow leak in the emergency line 6 the parts of the valve return to the position shown in the drawing sufficiently slowly for pressure to be delivered to the trailer brake chambers 10 at a rate slow enough to bring the vehicle to a gradual stop.