The parallel paths in each pod assure helium flow to the propellant tanks of that pod. They are energized open and spring loaded closed. With the switches in the GPC position, the valves are automatically controlled by the general-purpose computer during an engine thrusting sequence. The valves are controlled manually by placing the switches to open or close. The pressure regulators reduce the helium source pressure to the desired working pressure.
Pressure is regulated by assemblies downstream of each helium pressure isolation valve.
Each assembly contains primary and secondary regulators in series and a flow limiter. Normally, the primary regulator is the controlling regulator. The secondary regulator is normally open during a dynamic flow condition. It will not become the controlling regulator until the primary regulator allows a higher pressure than normal. All regulator assemblies are in reference to a bellows assembly that is vented to ambient.