The exhaust brake operates by restricting the flow of exhaust gases. This restriction causes the exhaust gases to be compressed, creating a back pressure that slows the engine and transmission. A small opening in the butterfly valve prevents the build up of excessive exhaust system pressure. This opening also protects the engine from damage during high exhaust gas flow levels.

During operation, air at line pressure is directed to the exhaust brake actuator. At the same time, the fuel supply to the engine returns to an idle condition. The air pressure in the actuator pushes against, and overcomes, the actuator return spring. This causes the push rod to extend and rotate the butterfly valve to the closed position.

When the air supply to the actuator is removed (rest condition), the actuator return spring retracts the push rod and returns the butterfly valve to the open position. This allows the exhaust gases to flow unrestricted. The fuel supply to the engine is also restored at this time.