Outflow valves L and R

[Guest pierre974]

Hi there,can someone explain the functionality of the Man Outflow L and R ?Should it be off ? When should it be turned on ?Last night I had some trouble with it and had to follow the abnormal procedure to manually close the valves...Need some expertise :-zhelp

[Guest Just747-400]

Cabin pressurization is controlled by regulating the discharge of conditioned cabinair through the outflow valves.Two outflow valves are installed at the rear of the cabin. The valves normallyoperate in parallel. Cabin altitude and full ventilation rates can be maintained byeither valve.There are two cabin altitude controllers, A and B. Each controller controls bothoutflow valves.Positive and negative pressure relief valves protect the fuselage against excessivepressure differential.The pressurization system has automatic and manual operating modes.In MAN, FMC altitude information is bypassed and the cabinaltitude controller uses internal rate schedules to control cabin altitude. Landingelevation limits are 1,000 feet below sea level to 14,000 feet above sea level.If both Outflow Manual switches are ON, all automatic cabin altitude controlfunctions are bypassed. For this configuration, one pack is selected off to ensurecabin doors may be opened regardless of the position of the outflow valves if anemergency evacuation is required immediately after landing.

[Guest pierre974]

Thanks for this accurate answer :-cool