On a commercial hot-water tank, why is the vacuum relief located on top of the tank?

On a commercial hot-water tank, why is the vacuum relief located on top of the tank?

• A. prevent collapse
• B. permit air entry
• C. regulate temperature
• D. conserve energy

Answer: (A)

Vacuum relief serves to prevent a negative pressure (vacuum) inside the tank when water is drawn off or cools, which could pull the walls inward and cause damage. The vent must respond as soon as a vacuum starts to form, and the upper portion of the tank is where the space above the water level first experiences negative pressure. Placing the vacuum relief on the top allows air from the atmosphere to enter easily into that upper space, breaking the vacuum before structural forces pull the tank inward. If the valve were located lower, it could be submerged or blocked by water and would not admit air when needed, defeating its purpose. So the top-location design ensures reliable air entry to protect against collapse.

Vacuum relief serves to prevent a negative pressure (vacuum) inside the tank when water is drawn off or cools, which could pull the walls inward and cause damage. The vent must respond as soon as a vacuum starts to form, and the upper portion of the tank is where the space above the water level first experiences negative pressure. Placing the vacuum relief on the top allows air from the atmosphere to enter easily into that upper space, breaking the vacuum before structural forces pull the tank inward. If the valve were located lower, it could be submerged or blocked by water and would not admit air when needed, defeating its purpose. So the top-location design ensures reliable air entry to protect against collapse.