Diverter Valve

Fig. 3 Air pump w/integral pressure relief valve:

Fig. 4 Typical diverter air bypass valve without pressure relief valve:

Fig. 5 Typical diverter air bypass valve w/pressure relief valve:

The diverter or air bypass valve, Figs. 4 and 5, when triggered by a sharp increase in manifold vacuum, shuts off the injected air to the exhaust and prevents backfiring during this richer period. On engine overrun the total air supply is dumped through the diverter valve muffler. At high engine speeds the excess air is dumped through the pressure relief valve located either in the pump assembly, Fig. 3, or the diverter valve, Fig. 5.
The check valves prevent hot gases from backing up into the hoses or pump,yet allow fresh air to circulate from the pump to the exhaust ports.