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Cab Inspection
Spring  Brakes

Equipment Operator Basic - Beginning construction equipment operators manual
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AIR BRAKES Air brakes use compressed air to make the brakes work. They provide a safe way to stop large vehicles when maintained and used correctly. The air brake system  is  composed  of  three  combined  braking  systems: the service brake system, the parking brake system, and the  emergency  brake  system. The service brake system applies and releases the brakes when you use the brake pedal during normal driving.  The  parking  brake  system  applies  and  releases the parking brakes when you use the parking brake control. The emergency brake system uses parts of the service and parking brake system to stop the vehicle in the event of a brake system failure. NOTE: The components of the air brake system are covered in chapter 3. Brake  Drums,  Shoes,  and  Linings Brake drums are located on each end of the axles. The wheels are bolted to the drums, and the braking mechanisms are located inside the drum. The brake shoes and linings are pushed against the inside of the drum, and this action causes friction that slows the vehicle and brings it to a stop. This friction creates heat on how hard and how long the brakes are used. Too much heat can stop the brakes from working properly. S-CAM  AIR  BRAKES.—  When  the  air  brake pedal is pushed, air is let into each brake chamber (fig. 7-10). Air pressure pushes the rod out, moving the slack adjuster, thus twisting the brake camshaft. This action turns the S-cam that forces the brake shoes away from one another and presses them against the inside of the brake drum. When the brake pedal is released, the S-cam rotates back and a spring pulls the brake shoes away from the drum, allowing the wheels to roll freely. WEDGE BRAKES.—  On  wedge  brakes,  the  brake chamber pushrod pushes a wedge directly between the ends  of  two  brake  shoes.  The  wedge  shoves  the  shoes apart and against the inside of the brake drum. Wedge brakes have either a single-brake chamber or two brake chambers that push wedges into both ends of the brake shoes. DISC BRAKES.— The air pressure in air-operated disc brakes acts on a brake chamber that produces movement of the slack adjuster, like on the S-cam brake. But instead of the S-cam, a “power screw” is used. The pressure of the brake chamber on the slack adjuster turns the  power  screw.  The  power  screw  clamps  the  disc  or rotor between the brake lining pads of a caliper. NOTE: Wedge and disc air brakes are less common and  the  heat  a  drum  can  take  without  damage  depends than the S-cam brake. Figure 7-10.—S-cam air brake. 7-9







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