Answer :
Final answer:
The trailer hand valve can be used to apply the spring brakes when the service brakes of a trailer fail.
The answer is option 2
Explanation:
This feature serves as an emergency measure to stop the vehicle in case of brake system failure. When the service brakes on a trailer fail to apply, the trailer hand valve, also known as the 'trolley valve' or 'parking brake', can be used to engage the spring brakes. The spring brakes work as an emergency measure, and their primary function is to stop the vehicle if the service brake system fails.
The trailer hand valve works independently of the foot brake system and allows the driver to apply the trailer brakes without applying the truck brakes. It's a very important tool for managing braking in various driving and parking situations.
The answer is option 2
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