Diverter Valve
The diverter valve is used to prevent backfiring in the exhaust system during sudden deceleration. The valve senses sudden increases in the intake manifold vacuum, causing valve to open and divert air away from exhaust system. This allows air from the air pump to pass through valve and silencer, out to atmosphere.
A pressure relief valve controls system pressure by diverting the excess pump outlet air (developed at higher engine speeds) to atmosphere through the silencer.