If storage tank screens are clogged with ice, what feature should be installed to relieve excess pressure and vacuum?

• A. Flap Valves
• B. Expansion Joints
• C. Check Valves
• D. Air Vents

Answer: (A)

The main idea here is to provide a way for the tank to exchange air so it doesn’t become over-pressurized or develop a vacuum when venting is blocked by ice. A flap valve is a one-way air relief device: it opens to vent excess pressure and closes to prevent backflow, yet it will also allow air in when negative pressure forms. In iced conditions, this one-way vent helps keep the tank pressure balanced even if the screens are clogged, protecting the tank from damage.

Other options don’t fit as well. Expansion joints absorb movement but don’t relieve air pressure. Check valves stop reverse flow but don’t provide air relief for pressure and vacuum changes. A standard air vent aims to vent air but can be ineffective if ice blocks it, whereas a flap valve specifically permits one-way venting to manage both high pressure and vacuum situations.