The main fuel valve is a butterfly-type valve, spring – loaded to the closed position, pneumatically oper­ated to the open position, and pneumatically assisted to the closed position. It is mounted between the fuel high-pressure duct from the fuel turbopump and the fuel inlet manifold of the thrust chamber assembly. The main fuel valve controls the flow of fuel to the thrust chamber. Pressure from the igni­tion stage control valve on the pneumatic control package opens the valve during engine start. As the gate starts to open, it allows fuel to flow to the fuel inlet manifold.


The main oxidizer valve (MOV) is a butterfly-type valve, spring-loaded to the closed position, pneu­matically operated to the open position, and pneu­matically assisted to the closed position. It is mounted between the oxidizer high-pressure duct from the oxidizer turbopump and the oxidizer inlet on the thrust chamber assembly.

Pneumatic pressure from the normally closed port of the mainstage control solenoid valve is routed to both the first and second stage opening actuators of the main oxidizer valve. Application of opening pressure in this manner, together with controlled venting of the main oxidizer valve closing pressure through a thermal-compensating orifice, provides a controlled ramp opening of the main oxidizer valve through all temperature ranges. A sequence valve, located within the MOV assembly, supplies pneu­matic pressure to the opening control part of the gas generator control valve and through an orifice to the closing part of the oxidizer turbine bypass valve.


The propellant utilization (PU) valve is an electri­cally operated, two-phase, motor-driven, oxidizer



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pressure-actuated to the closed position. Both pro­pellant bleed valves are mounted to the bootstrap lines adjacent to their respective turbopump dis­charge flanges.

The valves allow propellant to circulate in the pro­pellant feed system lines to achieve proper operat­ing temperature prior to engine start. The bleed valves are engine controlled. At engine start, a he­lium control solenoid valve in the pneumatic con­trol package is energized allowing pneumatic pres­sure to close the bleed valves, which remain closed during engine operation.

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