Page 156 - Driving Commercial Vehicles Manual+

8 air brakes

What you’ll learn
After reading this chapter you’ll be able to:

❏ identify the components of an air brake system
❏ explain how an s-cam foundation brake works
❏ describe what happens when one or more air brake system
components fail

❏ explain how trailer brakes are applied.

Why air brakes?

Air brake systems:
• use a much greater force to apply the brakes than hydraulic braking systems
do, which is needed to cope with the heavy loads of commercial vehicles
• are more tolerant to small leaks, which in a hydraulic system could result in
brake failure (an air brake system includes a compressor to generate more
compressed air as needed).

• are capable of stopping heavy commercial vehicles safely.

What’s compressed air?

Air can be compressed (squeezed) into a much smaller space than it would
normally occupy. The tires on a car are filled with compressed air to support
the weight of a vehicle.

Squeezing air into a smaller space increases the air’s resistance. This resistance
creates pressure, which can be converted into mechanical force to apply the
brakes. Air brakes generate more braking force than hydraulic brakes.

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