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).

Fig. 1, Parking Brake Control Knob

See Primary Air Brake System for further information about the brake system.