GB823160A - A valve device, in particular for fluid pressure braking apparatus for road vehicles - Google Patents

Abstract

823,160. Fluid-pressure brakes. WESTING- HOUSE BRAKE & SIGNAL CO. Ltd. June 7, 1956 [June 21, 1955], No. 17598/56. Class 103 (1). [Also in Group XXIX] A valve device for controlling fluid-pressure braking comprises apparatus for road vehicles in which the braking acts on the wheels of at least two axles of one vehicle or on the wheels of at least one axle of a tractor vehicle and on the wheels of at least one axle of a trailer vehicle, a piston control unit or member which by direct mechanical action closes the outlet valve 20 and opens the inlet valve 14 of a first valve group 15 to admit pressure fluid from a first source to a space 53. The pressure in this space 53 thereupon acts on a movable partition or piston 2 in opposition to a loading spring 36 housed in a chamber 56 open to the atmosphere. This spring acts in turn on a second movable partition or piston 3 to control by direct mechanical action the closure of the outlet valve 42 and the opening of the inlet valve 40 of a second valve group 41 whereby pressure fluid from a second source is applied to a space 47. The pressure in the second space 47 then acts on the piston 3 in opposition to the spring 36. The piston control unit comprises a closed cap 5 unitary with a piston 17 and slidable in a casing 1 against a spring 27 by means of a pedal-operated lever 9. The cap 5 provides a seat 13 for the inlet valve 14 and has a port 19 connecting a chamber 62 in the cap with a first high pressure supply port 49. One or more stops 21 are provided on the piston 17 so that if the piston 2 fails to move downwardly under fluid pressure to allow the inlet valve 14 to close it is moved positively by the stops. The piston 2 has a hollow hub 29 with ports 24 which connect the spaces 53, 56 when the outlet valve 20 is open. The lower piston 3 similarly has a hollow hub 31 with ports 34 to connect the spaces 47, 56 when the outlet valve 42 is open. A lost-motion connection comprising a head stem 25 slidable in the hub 31 is provided between the pistons 2, 3 so that the spring 36 is pre-compressed. A spring 43 stronger than the spring 27 acts on the piston 3 and normally maintains the piston 2 against a stop shoulder 57. Should the lower inlet valve 40 fail to reclose due to fluid continuously escaping from the space 47, the piston 3 engages an abutment 61. The spring 36 is then further compressed and the upper valve group 15 can still function. A higher pressure is maintained in the space 53 than the space 47 by an amount depending on the relative strengths of the springs 27, 43. The annular chamber 59 above the piston 17 is vented by a passage 60. The fluid pressure reaction below the piston 17 gives the operator a sense of feel. The unions 49, 51 are connected to separate pressure tanks and the unions 52, 54 to the brake cylinders associated with the rear and front axles, or those associated with a trailer and a tractor vehicle.