Non-Linear Vacuum Regulator Valve

There are 2 input ports on NLVR: intake manifold vacuum and carburetor ported vacuum. One outlet port connects to distributor vacuum unit. At curb idle, regulated vacuum is supplied to advance unit, when manifold vacuum is high and ported vacuum is very low. See Figure .

NLVR regulates vacuum signal so it is between these 2 vacuum source levels at idle. As engine load increases and vacuum signal is above 7.5 in. Hg vacuum, regulator valve switches to ported vacuum output.