What is the Johnson bar?
Answers
A hand valve that works the trailer brakes
A valve that indicates the fuel level
A valve that limits the amount of cargo
The Correct Answer and Explanation is :
The correct answer is: A hand valve that works the trailer brakes.
Explanation:
A Johnson bar, also known as a hand valve, is a device typically found on older tractor-trailer setups. It is used to control the braking system on the trailer portion of the vehicle independently of the truck’s main braking system. This feature is particularly important for situations where the driver needs to apply trailer brakes separately from the truck’s brakes.
The Johnson bar is a lever, usually located near the driver’s seat, that is manually operated. By pulling or pushing the lever, the driver activates the air brake system on the trailer. This provides the driver with more precise control over the braking of the trailer, which can be crucial for tasks such as parking or handling challenging driving conditions.
In modern commercial vehicles, the Johnson bar has largely been replaced by more advanced electronic systems that allow for more automated and efficient braking. However, it is still found in some older vehicles or in certain specialized applications where manual control over the trailer brakes is desired.
The use of a hand-operated valve like the Johnson bar is essential for maintaining safety when maneuvering a tractor-trailer combination, especially in situations where the trailer needs to be stopped or slowed without affecting the truck’s brakes. For example, when backing into a parking space or during emergency braking, the ability to apply only the trailer’s brakes can help prevent jackknifing and maintain better control over the vehicle.
Thus, the Johnson bar provides a crucial function in older or specialized vehicles, helping drivers manage the braking of the trailer independently from the truck’s braking system.