As far as I know there are no "damp" valves but there are dump valves which are similar to blow off valves for Forced Induction engines. When you close the throttle on an FI engine the turbo still wants to feed more air into the system and keeps pressurizing it (remember turbos are mechanical not electronic they don't have brains) and if it keeps going with no way to vent you get compressor surge and the pressurized air tries to spin the blades backwards, So what a dump valve does is it has a spring set to a certain preset pressure and if the pressure is exceeded it opens the valve and vents to the atmosphere. While it's a similar solution to the problem of compressor sure a blow off valve allows the turbo to "freewheel" when the throttle is closed thus equalizing the pressure.BOVs work at multiple pressure settings while dump valves work at only one. Now just to finish off on how to control boost there are CBVs (Compressor Bypass Valves) that cycle the air back before the turbo but after the Mass Airflow Sensor (don't wanna trip out your MAF).
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