2. BRAKING SYSTEM 2.3 TRAILER BRAKING SYSTEM 2.3.2 HYDRAULIC TRAILER BRAKING (EXPORT VERSION) N B D0022940 When the brakes are not operated the pressure at port B is null. When the operator applies the tractor brakes, the pressure in the circuit pilots the braking valve and the pressure at port B increases proportionally to the pressure in the tractor braking circuit. 10-24