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