When pedal 1 is depressed, valve spool 2 is shifted to the left and hydraulic fluid under pressure, delivered through port a, passes through passage b to the right end of cylinder 3. This moves piston 4 to the left. Fluid from the left end of cylinder 3 is delivered to the brake cylinders, performing the braking operation. The rod of piston 4 is linked to body 5 of the valve. As piston 4 travels, it moves valve body 5 to the left. When pedal 1 is released, body 5, in its motion, blocks off port a and stops fluid delivery to cylinder 3. Piston 4 stops moving. The left end of cylinder 3 is connected by axial passage d to the left end of body 5. The working pressure of the fluid in the left end of cylinder 3 resists motion of valve spool 2 with a force proportional to the degree of braking action. When pedal 1 is released, valve spool 2 is shifted to the right by the fluid pressure and connects passage b to the tank. This enables piston 4 to move to the right. At this, the brakes of the wheels are released.
$4299$CHP,Br$