Vacuum Restrictor: Description and Operation

Fig. 38 Vacuum restrictor:

The orifice type flow restrictor, Fig. 38, is used on some systems to control the flow rate and or timing characteristics to the following systems.
a. EGR valve timing (opening and closing).
b. Part throttle spark advance.
c. Purge system.
d. Thermactor system.
The flow rate through the restrictor is the same in both directions. If blocked, it should be replaced.