Vacuum Check Valve: Description and Operation

Fig.86 - Thermactor Vacuum Vent Valve:

Fig.87 - Thermactor Vacuum Vent Valve Schematic:

DESCRIPTION
This valve, Figs. 86 and 87, is used on some 1978-82 engines equipped with variable venturi carburetor. It provides the air for the thermactor retard delay valve and air bypass valve during idle modes to deactivate the thermactor system after a controlled period of time.

Application of vacuum from the carburetor to both ports of the thermactor vacuum vent causes the dump valve to seat and vacuum to be applied to the rest of the system. Removal of vacuum during idle modes results in unseating of the dump valve, opening of the vent and allowing air to enter the system to reduce the vacuum previously applied to the retard delay valve.