The Turbosmart BOV controller is an electronic device which controls the pressure signal to the BOV.
It works by detecting a negative voltage change in throttle position. It then energises a solenoid to vent all of the air out of the BOV cap, causing a pressure differential between the piston of the BOV and the cap which will vent pressure from the intake system.
Large diesel engines with larger turbochargers can experience compressor surge when coming off the throttle. The deceleration of the engine can be a restriction on the outlet of the turbocharger causing compressor surge.
This can be disastrous on a turbo system which is producing high amounts of boost. The BOV controller can vent this build up of pressure, protecting the turbocharger. This can reduce the amount of rebuilds on your turbocharger as well as improve acceleration between gears.