A tractor protection valve (Fig. 38) is usually mounted on the cab or chassis of the tractor. Figure 38. Tractor protection valve When the trailer-supply valve is open, air passes through the bottom of the tractor protection valve and charges the trailer through the supply line (also called the emergency line). When the pressure in the supply line reaches 45 psi, the service line port of the tractor protection valve opens. This allows application air pressure to travel down the service line to the trailer when a brake application is made. Note: Ask us a question or share a concern. Our goal is to get you the answer you need.
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A Normal position
Explaination Step 8: Supply air to the trailer - From cab, push in \"air supply\" knob or move tractor protection valve control from the \"emergency\" to the \"normal\" position to supply air to the trailer brake system. |