Patent ID: 8646852

Claim:
In a hydraulic arrangement, for use in a traction vehicle and trailer combination for controlling braking systems of each of said vehicle and trailer, including a source of pressurized hydraulic fluid, a tank, a trailer brake line coupled to said trailer braking system, a hydraulically activatable trailer brake valve connected to said source, tank and trailer brake line for selectively coupling said brake line either to said tank or to said source of pressurized fluid, a first control-pressure line coupled between said brake line and said brake valve for establishing a first control pressure at a first end of said brake valve, a control-pressure source, a second control-pressure line coupled between said brake valve and said control-pressure source for establishing a second control pressure at a second end of said brake valve, and an adjustable pressure-reducing valve arranged in said second control pressure line for controlling the second control pressure established in said second control pressure line, the improvement comprising: said control-pressure source being a control pressure used in said vehicle braking system; and said pressure-reducing valve including an adjustable prestressing force working in opposition to said second control pressure so as to place said pressure-reducing valve in a normally open position when said prestressing force exceeds said second control pressure.