An air relief valve is designed to discharge large volumes of air during filling and pressurizing, and to admit air when draining, but cannot ...?

• A. Also acts as a permanent filter to remove solids.
• B. Prevents any air from entering the system.
• C. Can release small residual air pockets during operation.
• D. Cannot release small residual air pockets while in operation.

Answer: (D)

Air relief valves are designed to vent large volumes of air as a system is filled and pressurized, and to admit air when the system is drained to prevent vacuum. They are not intended to filter out solids, nor do they prevent air from entering the system entirely. They are also not relied upon to continuously purge small residual air pockets that can form during normal operation. Those tiny pockets are typically addressed by separate devices (such as automatic air release valves) placed at high points. Because of this, the valve’s limitation is that it cannot release small residual air pockets while in operation—the statement describes its real-world behavior.