Which outflow valve can be manually closed on the 737?

Which outflow valve can be manually closed on the 737?

• A. Overboard exhaust valve
• B. Pressure relief valve
• C. Main outflow valve
• D. Negative pressure release valve

Answer: (C)

Airplane cabin pressure is controlled by venting cabin air overboard through outflow valves. The main outflow valve is the primary regulator and is designed to be manually closed, allowing crews to isolate the cabin from the outside environment during maintenance or abnormal situations. Other valves — the overboard exhaust valve and the negative pressure release valve — operate automatically to manage pressure changes and protect against over- or under-pressurization, and the pressure relief valve serves as a safety release. Closing these manually is not part of normal operation, so the valve that can be manually closed is the main outflow valve.

Airplane cabin pressure is controlled by venting cabin air overboard through outflow valves. The main outflow valve is the primary regulator and is designed to be manually closed, allowing crews to isolate the cabin from the outside environment during maintenance or abnormal situations. Other valves — the overboard exhaust valve and the negative pressure release valve — operate automatically to manage pressure changes and protect against over- or under-pressurization, and the pressure relief valve serves as a safety release. Closing these manually is not part of normal operation, so the valve that can be manually closed is the main outflow valve.