The Bendix® TP‑3® tractor protection valve is used in combination with the Bendix® PP‑3™ trailer supply valve on pre‑121 tractors, and the Bendix® PP‑7™ trailer supply valve – or the Bendix® MV-3® dash control valve – on post‑121 tractors. It contains a passage for trailer supply air and a service line shut off valve. It is normally mounted behind the cab, with the delivery line from the trailer supply valve connected into the tractor emergency port and a delivery line from the brake valve connected to the tractor service port. The trailer supply and service hoses are mounted in their respective ports in the TP‑3 valve.