Air Pump Systems
Air is drawn into the air pump through a centrifugal filter which is incorporated into the pump. From the pump the air is routed to the pressure relief valve (if equipped), where the excess air delivered by the pump at high engine RPM is discharged into the atmosphere when the line pressure exceeds 3.9 psi (.27 kg/cm2 ). The air is then routed to the diverter valve, where it depends on the engine coolant temperature and vehicle application.
On California 280 series, air is injected into the small catalytic converters when coolant temperature is below 63°F (17°C) or above 122°F (50°C). Air is injected into the cylinder head exhaust ports via the check valve when coolant temperature is between 63°F and 122°F (17°C and 50°C).
On all other models, air is discharged to the atmosphere when coolant temperature is below 63°F (17°C). Air is injected into the cylinder head exhaust ports via the check valve when coolant temperature is above 63°F (17°C).
From the exhaust ports, the exhaust gas/injected air mixture flows through the exhaust pipes and into the catalytic converter. The oxygen in the injected air combines with hot exhaust gas and this furthers the catalyst reaction in the converter.
System check valve(s) is used to prevent the flow of hot exhaust gases back into the system. Some systems also use an in-line check valve from intake manifold to thermo valve. This acts as a spark delay when vacuum levels are intermittently reached.