Fluid under pressure from the accumulator is delivered to the valve through port 1. Port 2 is connected to the brakes, and port 3, to the tank. When the brake pedal is depressed, stem 4 actuates spring 5 which presses ball a into its seat in piston 6, closing off channel d and opening valve member 7. This connects ports 1 and 2, and fluid under pressure is delivered to the brake cylinders. In releasing the brakes, when the force applied to stem 4 is reduced, the pressure of the fluid in the brake line, acting on ball a through axial channel d, pushes the ball to the left and connects the brake cylinders to the drain through port 3. Spring 8 returns stem 4 to its initial position.
$3627$SHP,Va$