A TP3DC-type tractor protection valve containing a double check valve, used to protect the tractor's air supply by automatically closing off air to the trailer in the event of a trailer breakaway or major air leak, preventing the tractor from losing its own braking air. It has 3/8" NPT control ports, 1/4" and 1/2" NPT stoplight switch and tractor control ports, and is built from die-cast zinc. It's a Bendix TP-3DC style aftermarket replacement, cross-referenced to Bendix numbers 065706, 109553, 109571, 109790, and 109791, among others.
