Vacuum Brake Booster: Description and Operation

Fig. 8 Delco-Moraine tandem diaphragm booster exploded view:

Fig. 9 Power head assembly exploded view. Delco-Moraine tandem diaphragm booster:

This unit has a vacuum power chamber that consists of a front and rear shell, a housing divider, front and rear diaphragm and plate assemblies, a hydraulic pushrod and a diaphragm return spring, Figs. 8 and 9.
The unit operates in much the same manner as the Single Diaphragm unit described previously. The diaphragm and plate assemblies utilize the pressure differential created by engine intake manifold vacuum and atmospheric pressure to assist the hydraulic pushrod.