Ports Closed - Under open throttle conditions where turbocharger boost pressure is required, the bronze BOV piston is held shut in order to supply the maximum amount of charge air to the engine

Primary Port Open - Under light load conditions where the throttle opening has been reduced or shut, the piston moves partially up the bore travel and opens the primary port to vent charge air back into the inlet tract. This ensures smooth engine operation and alleviates the rich condition and subsequent backfire when utilizing a BOV construction that vents100% of charge air to atmosphere.

Both Ports Open - Under high load conditions where the throttle has been shut, the piston travels fully so that both the primary and the wide mouth secondary ports open to vent the maximum charge air possible. Air vented through the primary port is routed back into the inlet tract. In addition, additional excess charge is air vented through the wide mouth secondary port to atmosphere.