Parking Brake Control Knob
All pneumatic-braked vehicles are equipped with a diamond-shaped parking brake control knob. See Fig.. Pull the knob to apply the parking brake. In air brake systems, before the parking brake can be released, the air pressure in either brake system must be at least 65 psi (448 kPa). See General Information for detailed operating instructions.
Fig. 1, Parking Brake Control Knob
Warning: If the vehicle is equipped with an air suspension system, do not move the vehicle with the air suspension deflated. Doing so could result in a loss of vehicle control, possibly causing personal injury and property damage.
Note: Chassis built with an air suspension dump option have an automatic feature that will not allow the suspension to be deflated unless the parking brakes are set. The suspension will automatically inflate when the parking brakes are released.