Air Brake System Components and Operation
Brake System Fundamentals (S-Cam Brakes and Air Systems)
Self-Energizing Brakes
Definition: Refers to which brake shoe bites into the drum harder.
Mechanism: If a drum rotates counter-clockwise, the force generated upwards on a brake shoe can push that shoe into the drum harder, enhancing the braking effect.
Brake Shoe Movement and Springs
Hydraulic vs. S-Cam Brakes: The presented visual example initially shows a hydraulic brake, not an S-cam brake.
Spring Function: In the displayed hydraulic brake, the bottom spring primarily holds components together and is not involved in major movement.
S-Cam Brake Springs: For an S-cam brake, the spring on the 'up' side (where the S-cam is located) only holds the shoe in its retracted (released) position, allowing it to return after braking. It does not actively contribute to the braking force during application.
Slack Adjuster Operation (Self-Adjusting Mechanism)
Purpose: Compensates for excess clearance between brake shoes and the drum, which occurs as brake linings wear.
Service Brake Application: When a service brake is applied, the push rod travels in a linear (straight) line.
Overstroke Detection: The system detects if the push rod travels past a angle (referred to as