In normal braking action, floating piston 1 is held against the seat in connection 2 by helical spring 3 and by the pressure of the fluid delivered through connection 4 from the main hydraulic system of the aircraft to the brakes through ports 5. When the emergency system is switched in, compressed air, entering through the channel of connection 2, pushes away piston 1, compressing spring 3 and closing off the main line. Compressed air flows through ports 5 into the brake cylinders, thereby braking the aircraft.
$3625$SHP,Va$