A TRAILER BREAKAWAY would result in a separation of the service line and the supply line. The sudden loss of air pressure in the supply line will trigger the relay emergency valve (25), which causes the trailer reservoir (2) to dump its air directly to the trailer brake chambers (26). This places the trailer brakes into emergency application.

The loss of pressure in the supply line also causes the trailer supply valve (24) to automatically shift to the close position.

The tractor brakes are operable without air loss because the tractor protection system has isolated the tractor.

The trailer brakes will remain applied until either the pressure in the trailer reservoir and lines is drained off, or the supply line is repaired and the system is recharged.