TP-3 tractor protection valve. P/N 279000. NSN 4820004363033. Used on some M939 series versions, M916A3, and M977 HEMTT. Also commercial truck applications.
Port pipe thread sizes are:
Tractor Service : 3/8”
Tractor Emergency : 1/4”
Trailer Service : 1/2”
Trailer Emergency : 1/2”
The TP-3 valve is used in combination with the dash mounted trailer supply valve to provide a means of controlling the two air connections
(service and emergency) leading to the trailer.
It automatically closes the service line in the event of a tractor trailer
breakaway or reduction of tractor system air pressure. Requires approximately 45 psi or greater from the tractor emergency line to open the service inlet valve.