An air suction valve (SAV) is a subsystem used to reduce emissions in the exhaust gases of internal combustion engines.
The exhaust manifold is configured in such a way that positive and negative pulses are produced during the operation of the cycle by designing it as a diffuser.
During deceleration, the engine vacuum rises and acts against the spring to push the shaft downwards, thereby blocking the opening through which atmospheric air is passed to the exhaust.
Used on the Honda Falcon NX4, mainly responsible for backfire or popping during deceleration when an open exhaust is added to the bike and if extra accessories is on vacuum circuit (Scottoiler, etc.).
The Royal Enfield Bullet, from year 2006-current, uses an Air Suction Valve to reduce emissions in its exhaust gases.