Under normal operation, how is the parking brake engaged in an air brake system?

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Multiple Choice

Under normal operation, how is the parking brake engaged in an air brake system?

Explanation:
In an air-brake system with spring brakes, the parking brake is held off by air pressure. When you let air out of the system, those springs are released to push the brake shoes onto the drums, which engages the parking brake. So letting air out is the way the parking brake is engaged under normal operation. The other actions don’t reliably cause the springs to apply the brakes: pumping the brake pedal builds service-brake pressure, turning off the engine isn’t the method for engaging parking brakes, and holding a parking-brake control isn’t how it’s normally engaged.

In an air-brake system with spring brakes, the parking brake is held off by air pressure. When you let air out of the system, those springs are released to push the brake shoes onto the drums, which engages the parking brake. So letting air out is the way the parking brake is engaged under normal operation. The other actions don’t reliably cause the springs to apply the brakes: pumping the brake pedal builds service-brake pressure, turning off the engine isn’t the method for engaging parking brakes, and holding a parking-brake control isn’t how it’s normally engaged.

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