In a trailer braking system, the trolley valve is used for which function?

The trolley valve is a crucial component in a trailer braking system used to apply service brakes. When the driver pulls the trolley valve, it sends air pressure to the trailer's brake chambers, engaging the service brakes. This allows for controlled braking, essential for safe operation during regular driving conditions.

Using the trolley valve effectively helps in managing the speed and stopping distances of the trailer, particularly in heavy loads. Proper understanding and use of this component is vital for any commercial driver's safety and operational efficiency.

The other functions listed do not accurately describe the role of the trolley valve. It does not activate emergency brakes, control air supply directly, or check fluid levels, which are tasks associated with other parts of the braking system or vessel maintenance. Understanding the specific functionality of the trolley valve is important for any driver who needs to operate trailers safely.