If your truck or bus has dual parking control valves, you can use pressure from a separate tank to: A- Balance the service brake system when you are parked. B- Release the spring emergency/parking brakes to move a short distance. C- Stay parked twice as long without using up service air pressure.
The Correct Answer and Explanation is :
The correct answer is: B- Release the spring emergency/parking brakes to move a short distance.
Explanation
Dual parking control valves are found in air-brake systems on heavy-duty vehicles like trucks and buses. These valves serve an important purpose by enabling the release of spring brakes (emergency/parking brakes) temporarily, using air from a separate auxiliary or reserve air tank. This can be particularly useful in situations where the vehicle needs to be moved a short distance, even if the main air pressure in the service brake system has been depleted.
In typical air-brake systems, spring brakes are applied automatically when air pressure drops below a certain threshold, usually due to a malfunction or depletion of air in the main reservoir. This feature ensures that the vehicle will remain safely parked if there’s a sudden loss of pressure, as the spring brakes activate to prevent unintentional movement. However, if the vehicle is blocking traffic or needs to be moved for repairs, the driver can use the dual parking control valve to release the spring brakes temporarily. This works by drawing air from the separate reservoir tank, which is independent of the main system, allowing for a limited amount of movement.
It’s important to note that this feature is not meant for regular driving but is only for emergency situations where the vehicle needs to be moved a short distance, such as repositioning it to a safer area or to a repair facility. The separate tank typically does not hold enough air for extensive movement, making this system more of a temporary solution. Regularly checking and maintaining all components of the air-brake system, including the auxiliary tank, is essential to ensure it functions properly when needed.