22.03 What is important about underground tank spill containers and overfill valves?

Tank spill containers for underground tanks are designed to accept and spilled product during the disconnect of the fuel delivery hose from the tank. Spill containers range for 20-75 liter capacity. The tank overfill prevention valve is installed through this same fill pipe connection to close automatically when the tank level reached 90% of capacity.

Spill containers should be designed to exclude surface water. The primary detail is to install the frame at 25-50 mm above the finished concrete grade with a 1 meter transition to the slab elevation. In addition, advanced spill containers have a tight seal design to eliminate water inflows. These designs are either a side seal traffic rated cover, or a water tight lid design located beneath a separate traffic rated cover.

Overfill prevention valves for underground tanks are designed for gravity delivery of fuel into the tanks. So they are rated at 100-170 kPA capacity. If fuel is to be pumped into the underground tank, then delivery pressures may be up to 700 kPA. A pressure rated overfill valve, as commonly used for aboveground tanks would be recommended in this case.