Figure 9-5. Vacuum Power Unit Cross Section

TM 10-3930-633-34

Figure 9-5. Vacuum Power Unit Cross Section

a secondary piston with two "back-to-back"

(2) A manually actuated control valve in-

tegral with the vacuum power diaphragm and

secondary seals, primary cup, protector, spring

plate hubs that controls the degree of power brake

and spring retainer; a piston stop screw and O-

application or release in accordance with the foot

ring seal; and two separate check valves (residual

pressure applied to the valve operating rod

p r e s s u r e ) , springs and tube seat retainers

through the brake pedal linkage. The control

mounted in the two outlet ports provide the

valve consists of a single poppet with an at-

operating components o f the two separate

mospheric port and a vacuum port. The vacuum

hydraulic systems. See TM 10-3930-633-12 for

port seat is formed in the hub of the rear

complete description and repair procedures on the

diaphragm plate. The atmospheric port seat is

master cylinder.

part of the valve plunger which moves within the

c. Operation.

valve housing hub of the diaphragm plates.

(1) The vacuum power diaphragm plates and

parts that make up the valve assembly are

(3) A hydraulic dual-system master cylinder

connected to the brake pedal through the valve

that provides two hydraulic fluid reservoirs, cast

operating rod. The valve operating rod is con-

integrally with and connected to the bore through

nected to the valve plunger which moves within

separate sets of compensating and fluid inlet (by-

the hub of the power diaphragm and plate

pass) ports. Both reservoirs are sealed by a

assembly. A valve return spring returns the valve

rubber diaphragm inside the baletype cover. A

plunger and valve rod to the released position

primary piston assembly with secondary seal,

when the brake pedal is released. The valve

primary cup, protector, spring, screw and spacer;

9-7