Although the operating pressure was maintained by an automatically controlled bleed valve once the plant had reached steady state, the valve could not be used during start-up, when there was no air feed, the plant being pressurised with nitrogen.
12.
In the Space Shuttle the main oxidizer and fuel bleed valves were used after shutdown to dump any residual propellant, with residual liquid oxygen venting through the engine and residual liquid hydrogen venting through the liquid hydrogen fill and drain valves.
13.
During start-up the bleed valve was normally isolated and there was no route for excess pressure to escape; pressure was kept within acceptable limits ( slightly wider that those achieved under automatic control ) by operator intervention ( manual operation of vent valves ).
