Thermal Vacuum Valve (TVV)
TVV is mounted on intake manifold. It is connected in series with carburetor vacuum port and EGR valve. Valve operation motive force is provided by a bimetalic distortion.
The valve remains closed and EGR system does not operate as long as coolant temperature remains below a specified level. If coolant temperature rises above a specified level, valve will open and EGR system will begin to operate.