Specifications

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4.3 Vacuum booster
Using the vacuum booster with the power cylinder can make the forklift truck
brake.
Vacuum booster boosts brake fluid by the pressure difference between the
vacuum pressure and the atmospheric pressure, higher oil pressure of the brake
cylinder can reduce the intensity of the drivers and improve the brake security.
4.3.1 Vacuum booster and master cylinder
The forklift trucks use 9″+10″dual diaphragms vacuum booster and master
cylinder, its outline and internal construction is as shown in Fig. 4.5 and Fig. 4.6
separately. The operation of vacuum booster and master cylinder is as follow:
(1) Before operation—brake pedal is not depressed
As the vacuum booster doesn’t work, cone spring 3 pushes control valve push
rod 1 and piston 5 to the limit position, air valve 4 is pushed down on piston 5 by cone
spring 6, and thus air valve port is closed.
(2) Brake operation
A. As the brake pedal is pressed, pedal force enlarged by lever acts on control
valve rod 1，pushes the cone spring 3 and piston 5 shift forward, through feedback
disk 10 and push rod 13, some pressure comes into being in master cylinder and
transmits to the operation cylinder, at the same time the air valve 4 shifts forward
along with piston 5, it gets in touch with vacuum valve port of the control valve body 7
and closes it, thus the front and rear chamber of the air chamber is separated.
B. As the control valve rod 1 shifts forward, piston 5 departs from air valve 4, air
charges into the rear chamber through the filter cushion 2, control valve chamber and
channel B, thus pressure difference between two chambers effects the acting force, a
fraction used for cone spring 3, the others used for feedback disk and master cylinder.
(3) Release the brake pedal
A. During the course of pressing the brake pedal, air enters into the front and rear
chamber through the air valve port, the control valve body further shifts forward; When
the brake pedal stays at a certain position, control valve body shifts forward to close
the air valve port, the vacuum booster is in a balance condition and the wheel brake is
in the state of brake.
B. When releasing the brake pedal, return spring 14 and cone spring 3 push the