To test the proper function of the tractor protection valve:. Verify that the system is at ______ pressure, charge the trailer by opening the _____ ______ valve, make a brake application and _____ it, (use a hand brake valve if ______. Disconnect the _________ (______) line (there will be a loss of air.) Now disconnect the _____ (__________) line.

Control (service) air will stop _______ and supply (emergency) air should continue to be ______, depending on the system.

Reconnect the supply (emergency) line and again service air will be ______. This tests the proper opening and closing operation of the _______portion of the valve. A tractor protection valve with a broken _______ _______ will not close the valve and will cause loss of air during normal brake applications if operating the tractor without a ________ .