Parking Brake Control Valve
Note: See Chapter 15 Brake Systems for detailed information about brake systems.
The yellow diamond-shaped knob operates the parking brake valve. See Fig.. Pull the knob out to apply both the tractor and the trailer spring parking brakes. Push both the parking brake and the trailer air supply knobs in to release the tractor and trailer spring parking brakes. Before the spring parking brakes can be released, the air pressure in either air brake system must be at least 65 psi (447 kPa).
If the trailer is not equipped with spring parking brakes, pull the parking brake valve out to apply the tractor parking brakes and the trailer service brakes.
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Trailer Air Supply Valve (red knob)
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Parking Brake Control Valve (yellow knob)