How far from the top of a tank should the relief valve be located?

How far from the top of a tank should the relief valve be located?

• A. Three inches
• B. Six inches from the top
• C. Nine inches
• D. Twelve inches

Answer: (B)

Relief valves vent into the tank’s gas space and need a little clearance above the liquid surface so the discharge isn’t blocked or fouled and the vent path can be routed safely. Placing the valve about six inches down from the top provides a small, reliable vapor space for the valve to release into, while keeping the discharge line clear of the lid or any top fittings. If it were much closer to the top, splashing or liquid could interfere with the valve or its outlet; if it were much farther down, the discharge could be too close to the liquid surface, risking contact with liquid and a less effective vent. Six inches from the top is a practical, standard compromise for proper venting.

Relief valves vent into the tank’s gas space and need a little clearance above the liquid surface so the discharge isn’t blocked or fouled and the vent path can be routed safely. Placing the valve about six inches down from the top provides a small, reliable vapor space for the valve to release into, while keeping the discharge line clear of the lid or any top fittings. If it were much closer to the top, splashing or liquid could interfere with the valve or its outlet; if it were much farther down, the discharge could be too close to the liquid surface, risking contact with liquid and a less effective vent. Six inches from the top is a practical, standard compromise for proper venting.