Abstract: A time delay valve used in vacuum systems of internal combustion engines to significantly reduce exhaust emission pollutants. The valve includes a resilient valve disk with an orifice therethrough. An enlarged cavity is provided adjacent the valve disk into which either a spacer ring or spring may be inserted. In one mode, with the spacer ring inserted, the time delay valve regulates the change rate of both vacuum increase and vacuum decrease across the valve. In an alternative mode with the spacer ring replaced by a spring, the time delay valve regulates only the change rate of vacuum increase across the valve.

Abstract: An improved modulating air control valve which intermittently introduces air into the intake manifold of internal combustion engines as a function of the vacuum differential between the intake manifold and the ported vacuum at the carburetor. The valve includes a unidirectional flow valve which prevents hydrocarbon gases contained in the intake manifold from deteriorating the internal diaphragm of the valve.