Vacuum Regulator

Fig. 34 Two port vacuum regulator:

Fig. 35 Three port vacuum regulator:

Fig. 36 Four port vacuum regulator:

The two port vacuum regulator, Fig. 34, is used to provide a constant output signal when input signal is greater than the calibrated level. At levels below the regulator calibration, the output signal will equal input.
Three port, Fig. 35, regulators and four port, Fig. 36, regulators used on some vehicles, are used to control the vacuum advance to the distributor. During engine idle conditions, the manifold vacuum signal is reduced to a constant output signal. Off idle, the output signal equals the spark port.