2.1.2 Master cylinder
The master cylinder contains valve support, check valve, return spring, primary cup,
piston and secondary cup, which are all kept in place with stop washer and stop wire. The
exterior of the cylinder is protected from dust by means of a rubber dust cover. The piston
is actuated through the push rod by operation of the brake pedal. As the brake pedal is
pressed, the push rod pushes the piston forwards. The brake fluid in the cylinder flows
back to the reserve tank through the return port until the primary cup blocks up the return
port. After the primary cup passed through the return port, the brake fluid in the cylinder is
pressurized and opens the check valve, flowing through the brake pipeline to the operating
cylinder. Thus each operating cylinder piston is forced outwards. This compresses or
impacts the disc brake to slow or stop the truck. Meanwhile, the cavity caused behind the
piston is filled with brake fluid led through the return port and inlet port. When the brake
pedal is released, the piston is forced back by the return spring. At the same time, the
brake fluid in each operation cylinder is pressurized by the return spring, returning into the
master cylinder through the check valve. With the piston in its original position, the brake
fluid in the master cylinder flows into the reserve tank through the return port. The brake
fluid in the brake pipelines and operating cylinders has a residual pressure proportioned to
the set pressure of the check valve, which makes each operating cylinder piston cup
securely seated to prevent oil leakage and eliminates a possibility of air locking when the
truck is sharply braked.
Fig.2-2 Master cylinder
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