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Technology: Engineering Our World
From this example, you can see that the effort acting on a piston from
a liquid under pressure depends on the area of the piston. The larger the
area is, the larger the effort will be. However, the distance moved by the
larger piston will be less than the distance moved by the smaller piston.
In Figure 8-54, the smaller piston moves four times the distance of the
larger piston.
The hydraulic brake system on passenger cars operates using the same
principles as the hydraulic lift. See Figure 8-55. Using the brake pedal, a
driver applies a small effort to the piston. Hydraulic fluid is transmitted
through the brake lines to a larger piston. The larger piston forces the
brake pads and shoes against the discs and drums. The brake systems of
large trucks, buses, and trains are often pneumatically operated.
Among the many common applications of hydraulic power are dentist
and barber chairs, door closers, and power steering. Common applications
of pneumatic power include a variety of tools such as air drills, screw -
drivers, and jackhammers. Sometimes hydraulic and pneumatic systems
are combined. For example, air pressure forces hydraulic fluid to raise the
lift in a garage, as shown in Figure 8-52B.
Because of their many advantages, most industries use hydraulic and
pneumatic systems. These advantages include the ability to:
• Multiply a force using minimal space
• Transmit power to wherever pipe, hose, or tubing can be located
• Transmit motion rapidly and smoothly
• Operate with less breakage than occurs with mechanical parts
• Transmit effort over considerable distance with relatively small loss
Piston
movement
Piston
movement
gure 8-54. In this hydraulic lift, the large
movement in the piston on the right causes
a smaller movement in the piston on the left.
Why is this an advantage?
Brake
pedal
Small
effort
moving
piston
a larger
distance
Disk
pad
Larger effort moving piston
smaller distance
gure 8-55. An automobile braking system
is an example of a hydraulic system.