How do you check protection valve on tractor tralior?

With the vehicle aired up, push in the clutch, put the vehicle into gear, and turn off the ignition (leaving the tractor protection valve pushed in). When the motor is shut off, release the clutch. The motor will be off and the vehicle will be in gear, which will prevent you from rolling.

Now, you simply pump on the brake pedal. This will reduce air pressure in the tanks (which won't build back up, as the motor is cut off). The tractor protection valve should pop out automatically when air pressure gets below 60.