Abstract: In a braking axle driven by a wheel of a trailer vehicle, wherein an axle-driven pumping mechnism is used to pressurize a volume of hydraulic fluid in response to a braking command, the fluid pressure activates a turbine which in turn drives a cooling fan aimed at a radiator used to dissipate the heat accumulating into the hydraulic fluid. The coaxially circular arrangement of the pumps, control valves and other components of the system yields a simple, efficient and sturdy mechanical structure that can withstand very high internal fluid pressure with a limited and controllable leakage rate.