Propellant Pressurization Helium System
The propellant pressurization helium system supplies gas to pressurize the liquid oxygen and ammonia tanks.
This helium is contained in the supply tank, within the center section of the liquid oxygen tank and is pressurized to 3600 psi. The helium flows to the normally open pressure regulators of the liquid oxygen and ammonia supply tanks.
The two regulators are actuated by helium pressure (from the engine and propellant helium control system) to the closed position when the vent, pressurization, and jettison control lever [11, fig. 5-4] is at VENT. When the control lever is placed at PRESSURIZE or JETTISON, the regulators open and helium pressure flows to the liquid oxygen and ammonia tanks.
The regulators reduce the helium pressure to 48 psi before it enters the liquid oxygen and ammonia tanks.
When the liquid oxygen and ammonia tanks are pressurized, the propellants are forced through the feed lines to the main feed shutoff valves.
The propellant source pressure gauge [69, fig. 5-1], on the instrument panel, is powered by the 26-volt AC bus. The gauge indicates pressure in the cylindrical helium tank for liquid oxygen and ammonia tank pressurization.The gauge is calibrated from 0 to 4000 psi in increments of 100 psi.
Note: This gauge is modified in the X-15A-2 airplane. Refer to "X-15A-2 Propellant Supply System for details.