GB1205718A - Relay valve - Google Patents

Abstract

1,205,718. Brake relay valves; drivers' valves. BENDIX CORP. 4 Dec., 1968 [28 Dec., 1967], No. 57621/68. Heading F2F. A relay valve comprises normally closed valve means located within a valve housing between an inlet chamber connected to a high fluid pressure source and an output chamber connected to pressure-responsive receiver means, and a movable pressure-responsive valve actuating member operatively arranged between the output chamber and a control chamber supplied with a control fluid pressure, the valve actuating member having passage means therethrough controlled by a return check valve operative to prevent fluid flow from the control chamber to the output chamber. As shown, the valve means is 66, 68, the inlet chamber is 70, the source is 17 or 104, the output chamber is 54, the receiver means is trailer brakes 24, 26, the actuating member is 48, 76, the control chamber is 50 (supplied at 52), the passage means is 78 and the return check valve is 80. Before actuation, hydraulic supply pressure is transmitted by pump 17 along conduit 28 to bore 40 in relay valve housing 36 where it opens poppet valve 118-114 governed by a light spring 122. The hydraulic chamber of an accumulator 104 is thus pressurized. Hydraulic pressure is also transmitted from bore 40 along passage 98 to a chamber 96 to bias an emergency control piston 92 into engagement with a plug 46. On actuation of brake pedal 12, control valve 10 is operative to supply braking pressure to conduit 18 leading to the tractor brake system and to conduit 32 leading to the relay valve 20. Pressure in inlet control chamber 50 builds up because of the normally-closed check valve 80 and accordingly moves actuating piston 48 to the left against the force of return spring 90. Control plunger 76 engages ball valve 66 whereby passage 78 in the integral plunger and piston is closed. Further displacement of piston 48 moves the ball 66 away from its seat 68, so that hydraulic fluid from supply line 28 and/or accumulator 104 via inlet chamber 70 supplies output chamber 54 and thence, via passages 56 and 58 and conduit 22, the trailer brake mechanisms 24, 26, until the pressure in output chamber 54 substantially equals the control pressure in the inlet control chamber 50. On brake release, the pressure in the trailer brake system urges control piston 48 to its release position and opens the check valve 80 to permit return of hydraulic fluid to reservoir 16 via perforated plate 84, inlet control chamber 50, conduit 32 and control valve 10. The valve 80 maintains a given residual pressure in the trailer brake system. Upon failure in supply conduit 28, pressure falls in bore 40 and chamber 96, so piston 92 is biased by spring 100 to the left. A projection 102 on piston 92 thereupon engages plate 84, thereby forcing the actuating piston 48 to the left for operation of the trailer brakes as before. Sufficient pressure for such operation is ensured, despite failure of conduit 28, by provision of the accumulator 104, in which a relatively high pressure is maintained by provision of a further valve in bore 40, operative in the reverse direction to poppet valve 118-114, and constituted by the movable "seat" member 112 (of the poppet valve), a fixed seat 114, and a relatively heavy compression spring 116.