Final answer:
The trailer hand valve, meant for operating the trailer brakes, should not be used while driving due to the risk of the trailer skidding. It should only be used for testing, adjusting, or parking the trailer.
Step-by-step explanation:
The trailer hand valve, also known as the trolley valve or Johnson bar, is specifically designed to work the trailer brakes.
It is important not to use this valve while driving as it can cause the trailer to skid, which can be dangerous. The appropriate use of the trailer hand valve is limited to situations such as testing the trailer brakes, when adjusting them, or when you need to park the trailer without using the tractor's brakes.
In regular driving conditions, the brake pedal should be used to ensure that the brakes are applied evenly across all wheels to prevent the trailer from skidding and to maintain control over the vehicle.
The trailer hand valve, also called the trolley valve or Johnson bar, works the trailer brakes. It should only be used when the vehicle is parked or stationary. Using the hand valve while driving can be dangerous because it may cause the trailer to skid.