283,922. Bragg, C. S., and Kliesrath, V. W. Jan. 20, 1927, [Convention date]. Fluid - pressure. - A control valve for brakes on a trailer vehicle operated by the suction of the tractor engine is actuated by the closing in of the trailer on the tractor when the tractor brakes are applied so as to apply the trailer brakes. In one arrangement the actuator or cylinder for the trailer brakes is connected to that of the tractor brakes so that both sets of brakes may be applied simultaneously by the valve mechanism of the tractor actuator and an additional valve is 'provided which is actuated to increase the application of the trailer brakes if these have already been applied, should the trailer overrun the tractor or to release them or prevent their application if the trailer tends to lag unduly behind the tractor. As shown in Figs. 1 and 2, the brake equipment comprises actuators P, P<1> connected respectively to the brakes a, a<1>, b, b<1> of the tractor A and trailer B. The actuator P is of the kind described in Specification 262,067, comprising a pair of valves 40, 41 dis. posed in a chamber formed in the piston 3 and slidably mounted on a rod 20 connected to the pedal 88. The valves are urged apart by spring and are actuated by projections on the rod. 20 which slides in the piston rod 5 connected to the tractor brakes by the link 78 and shaft 76. The forward piston chamber is connected to the engine suction pipe 61 by the pipe 62 in which non-return and restricting valves 62b, 62a are disposed. Normally the valve rod 20 is urged by the pedal spring 89 or a spring 23 or both to the position shown in which the valve 40 is unseated and the rear piston chamber is exhausted by way of the passages 34, 35. If the pedal is depressed the valve 40 is seated and the valve 41 is unseated to admit air to the rear chamber through passage 29 and ports 21 thereby applying the brakes. H the movement of the pedal ceases the continued movement of the piston causes the seating of the valve 41 and the brakes are held applied. The operator may exert a direct effort on the piston by the engagement of collars 44, 45 on the valve and piston rods. Pipes 90, 91 91<1> extend between the respective piston chambers of the actuators P, P<1> and a valve 94 is disposed in the pipe 91, 91<1> and has also a connection 90c with the pipe 90. A Bowden or other connecting means 96 extends from the arm 95 of the valve 94 to a point on the. tractor, preferably with the interposition of a spring 96a. With the vehicles at the normal distance apart the arm 95 and the valve are held in the position shown, in which the connection of the pipes 91, 91<1> is maintained through the passage 94a and similar pressure conditions are established in the piston chambers of the actuators P, P<1> so that the brakes on the tractor, and trailers are simultaneously operated. With the brakes thus simultaneously applied, should the trailer overrun the tractor by reason of its being heavily loaded the release of the tension in the connection 96 permits the spring 100 to turn the valve to a position such that the pipe 91<1> is connected through a cavity 94c and port 93c to atmosphere so that the trailer brakes are fully applied. The trailer brakes are similarly applied by the overrunning of the trailer if the tractor brakes are not applied. If on the other hand the trailer tends to lag sufficiently to compress the spring in the coupling by which it is connected to the tractor, the increased pull on the connection 96 moves the valve 94 to a position in which the pipe 91<1> is cut off from the pipe 91 and is connected to the pipe 90 by the cavity 94b so that the pressures in the chambers of the actuator P<1> are equalized and the tractor brakes are thus released or their application prevented if they are not already applied. The release of the trailer brakes in this way will be effected if the trailer is only lightly loaded. The pipes 90, 91 are provided with cut-off valves 90a, 91a, to permit the use of the actuator P when the tractor is being run alone. According to another arrangement the trailer actuator P<1> is not connected to the tractor actuator if such is provided. In this case the through passage 94a in the valve 94 is dispensed with and the valve normally connects the pipes 90, 91<1>. If the trailer overruns the tractor, as when the tractor brakes are. applied the pipe 91<1> is cut off from the pipe 90 and is connected to atmosphere, thus applying the trailer brakes.