How many pressurization valves are in the pressurization system?

• A. Two
• B. Three
• C. Four
• D. Five

Answer: (B)

In pressurization, you need both regulation and protection. The cabin is vented to the outside through two independent outflow valves, which the system uses to control the rate at which air leaves and thus maintain the desired cabin pressure. Having two valves provides redundancy so a single valve failure won’t prevent maintaining safe pressure. In addition, a relief valve is included to protect against overpressure by opening if the cabin pressure would otherwise rise too high. Put together, that’s two outflow valves plus one relief valve, totaling three valves in the pressurization system. Four or five valves would be more than needed for normal operation, and having only two would leave no dedicated overpressure protection.