Helium is supplied to the Reaction Control System propellant with the helium pressure used drive the propellant out of the bladders at the proper feed rate to the R-4D reaction control engines in the quads.
The helium isolation valves between the helium tank and pressure regulators contain two solenoids: one solenoid is energized momentarily to unlatch the valve, and spring pressure and helium pressure forces the valve closed. The helium isolation valves in each quad are individually controlled by their own individual SM RCS Helium switch on Command Module panel MDC-2.
The momentary OPEN position energizes the valve into the magnetic latch (open). The momentary CLOSE position energizes the valve to unlatch the magnetic latch (closed). The center position removes electrical power from either solenoid. The valves are normally open in respect to system pressure substantiating the magnetic latching feature for power conservation purposes during the mission in addition to prevent overheating of the valve coil.
Thanks to Scott Schneeweis for the technical description of this interesting artifact.
Accessory Products Company
Solenoid Valve, Helium
part # 512000-0014
serial # 100200000059
control # ME 284-0336-0014
contract # NAS 9-150
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