What is the purpose of the cylinder valve on an SCBA?

• A. To regulate inhalation pressure to maintain a safe breathing rate.
• B. To purge moisture from the air line.
• C. To read cylinder temperature.
• D. To allow controlled release of high-pressure air from the cylinder and to shut off air flow when not in use.

Answer: (D)

The cylinder valve controls and isolates the high‑pressure air coming from the cylinder. When you open it, air flows to the regulator and then to your facepiece; when you close it, the air flow stops. This provides a quick, reliable way to start and stop the breathing air and to shut off the supply for safety during handling or storage. The regulator downstream is responsible for delivering breathable pressure to you, not the cylinder valve. Purging moisture or reading cylinder temperature aren’t functions of this valve; those are handled by other parts of the system.