DECEL Valve System: Operation
Conventional decel valve is operated by a diaphragm subjected to atmospheric pressure on one side (through small hole in bottom of valve) and manifold vacuum on other side. A small diameter pipe connects valve to a system of fuel and air bleed jets in carburetor. When valve is opened (caused by high manifold vacuum) air/fuel mixture is drawn from carburetor and enters intake manifold. This additional air/fuel mixture results in a considerable reductions of hydrocarbons and carbon monoxide emissions.
The speed modulated decel valve uses a vacuum solenoid to control operation of decel valve. Decel valve is operational when vehicle is decelerating above 11 MPH. When decelerating below 11 MPH, vacuum solenoid closes, stopping vacuum to decel valve.
The A/C modulator decel valve uses a vacuum solenoid (controlled by the A/C on/off switch) as an interlock to prevent operation of the decel valve when the A/C is off.