Vacuum Amplifier: Description and Operation

EGR VACUUM AMPLIFIER





Some models use a vacuum amplifier to control EGR. The amplifier works like a "vacuum relay" which uses engine vacuum to operate the EGR valve but is controlled by weak "venturi vacuum" produced by a special restriction near the throttle plate.

At idle there is not enough control vacuum to operate the amplifier; at part throttle control vacuum trips the amplifier and allows engine vacuum to operate the EGR valve; at full throttle the EGR valve is closed because engine vacuum has dropped off even though control vacuum continues to increase with engine speed.