During normal operation of a positive pressure, open-circuit self-contained breathing apparatus (SCBA), what should the bypass valve do?

In the context of a positive pressure, open-circuit self-contained breathing apparatus (SCBA), the bypass valve is designed to ensure that the breathing apparatus functions correctly and safely during operation. When the SCBA is in normal use, the bypass valve should be fully closed.

This design allows the SCBA to maintain a positive pressure within the mask, which is crucial for preventing contaminants from entering the breathing zone. When the valve is closed, all air supplied to the user comes directly from the tank through the regulator, ensuring that the flow remains steady and that the individual is receiving a consistent supply of breathable air.

Keeping the bypass valve closed during normal operation also ensures that any emergency air supply or additional pressure from the tank is maximally utilized for breathing, rather than escaping through the bypass. This setup is critical in hazardous environments where maintaining a secure source of clean air is essential for the safety of the user.