What does a non-return check valve do?

• A. Prevent water from entering the helmet if air supply fails
• B. Allows water to enter the helmet
• C. Regulates the water temperature
• D. Delivers emergency air

Answer: (B)

A non-return check valve acts like a one-way gate for the fluids in the system. It is placed so that air can flow toward the helmet, but water or other fluids cannot flow back toward the surface equipment. In diving life-support setups, this protects the helmet and the surface air supply from backflow, especially when pressure changes or the supply is interrupted. So the valve’s job is to prevent water from moving backward into the system, not to let water into the helmet. If a choice says water entering the helmet is allowed, that describes the reverse direction of flow and isn’t how a one-way valve is used in standard diving configurations.