What Are Ball Float Valves?
Ball float valves (see illustration on the right) are placed at the bottom of the vent line several inches below the top of the UST. The ball floats on the product and rises with product level during delivery until it restricts vapor flowing out the vent line before the tank is full. If all tank fittings are tight, the ball float valve can create enough back pressure to restrict product flow into the tank which can notify the driver to close the truck’s shutoff valve. However, if the UST has loose fittings, sufficient back pressure may not develop and will result in an overfill. Note: Manufacturers do not recommend using ball float valves with suction piping, pressurized delivery, or coaxial Stage I vapor recovery.
