By-Pass Valve

During normal operation, intake manifold vacuum positions by-pass valve diaphragm and stem upward to allow air pump air to reach exhaust ports. When manifold vacuum changes (rises with deceleration or drops with acceleration), idle vacuum valve momentarily cuts off vacuum to air by-pass valve. By-pass internal spring pulls stem and diaphragm downward and air pump air is dumped to atmosphere.

In case of sudden pressure buildup in valve, lower portion will unseat to dump part of the pressure while upper portion is also unseated to allow some air to exhaust ports to continue normal air pump system operation.

Some systems are equipped with air by-pass valve with an integral vacuum differential function and vacuum vent valve. When vent is blocked, valve functions as timed by-pass valve to control air flow to exhaust ports. When vent is open to atmospheric pressure and vacuum is applied to source port (4 in. Hg or more), valve goes immediately to dump mode.