Storage tanks should also have _________ to relieve excess pressure and vacuum if the screens become blocked.

• A. Flap Valves
• B. Check Valves
• C. Air Vents
• D. Pressure Relief Valves

Answer: (A)

Relieving both excess pressure and vacuum in a storage tank when airflow paths are blocked requires a device that can move air in and out while keeping liquids out. A flap valve fits this role because it sits in the vent line and stays closed to keep contaminants out, but opens when interior pressure becomes higher than atmospheric to vent air, and also allows air to enter if a vacuum develops. This bidirectional relief protects the tank from damage when screens block normal airflow.

Other options don’t provide this same dual function. A check valve mainly prevents backflow of liquid and doesn’t reliably vent for pressure changes. A pressure relief valve focuses on releasing excess pressure but doesn’t address vacuum conditions. An air vent helps release trapped air but isn’t designed to permit controlled bidirectional relief in a blocked-screen scenario.