Air suction valve

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An air suction valve (SAV) is a subsystem used to reduce emissions in the exhaust gases of internal combustion engines.

[edit] Working principle

When an engine exhaust valve is open, the pressure in the exhaust manifold is higher than atmospheric pressure. 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.

The SAV has three openings: one is connected to the manifold vacuum, another is connected to the exhaust pipe and the third is open to the atmosphere. When a negative pulse is induced in the exhaust, air from the atmosphere enters the exhaust manifold through a one-way reed valve and serves to oxidize the carbon monoxide and hydrocarbons in the exhaust.

[edit] Air cut valve system

This system consists of a spring-loaded diaphragm, and a shaft which is attached to the bottom. A manifold vacuum is applied over the diaphragm where the shaft end is towards the opening of the atmosphere.

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.

Though there is a negative pulse during deceleration, the manifold vacuum blocks and cuts off the air to the exhaust manifold.