Switch/Relief Valve
Switch/relief valve is a dual function valve. Valve directs air injection flow to either exhaust ports or to downstream. On cold start, manifold vacuum signal is sent to switch/relief valve and air supply is directed to exhaust ports. Once engine is warmed, air supply is directed downstream.
Valve also regulates by controlling output of air pump at high speeds. Valve is controlled by manifold vacuum and with either a CVSCO valve and/or a vacuum solenoid. A bleed orifice in solenoid allows vacuum signal to go to zero. Without vacuum signal, most air supply is diverted to atmosphere. See Fig 1 .