When should you use the valve to park a combination vehicle?

Using the valve to park a combination vehicle is not recommended because it can lead to potential safety hazards. The parking valve is intended to release air from the brakes and can result in loss of braking power if engaged accidentally while the vehicle is in motion. Proper parking procedures require that the vehicle be secured using the service brakes and the parking brakes, rather than relying on the valve.

It is essential to fully engage the parking brake when the vehicle is stationary to ensure it does not roll or move unexpectedly. This is especially important when the vehicle is parked on a slope or uneven ground, where relying solely on other systems could cause issues. Remembering to use parking brakes instead of the valve ensures greater safety and stability for both the vehicle and those around it.