71SO Overfill Prevention Valve

The CARB-certified OPW 71SO vapor-tight Overfill Prevention Valve is  designed to prevent the overfill of underground storage tanks by providing a positive shut-off of product delivery. The shut-off valve is an integral part of the drop tube used for gravity  filling. The OPW 71SO allows easy installation (without breaking concrete) and requires no special manholes.

The OPW 71SO is a vapor-tight two-stage shut-off valve. When the liquid level rises to about 95% of tank capacity, the valve mechanism is released, closing automatically with the flow. This reduces the flow rate to approximately 5 gpm through a bypass valve.  The operator may then stop the filling process and disconnect and drain the delivery  hose. As long as the liquid exceeds the 95% level, the valve will close automatically each time delivery is attempted.

If the delivery is not stopped and the liquid rises to about 98% of tank capacity, the bypass valve closes completely. No additional liquid can flow into the tank until the level drops below a reset point.

Advantages of Overfill Prevention Compared to Overfill Warning Systems:

  • Completely Automatic Operation – does not rely on the alertness or speed of response of the delivery attendant for certainty of overfill prevention.
  • Keeps the Top of UST “Dry,” per EPA Requirements – eliminating possible leaks at loose bung fittings and the need for double containment on vent lines.
  • Does Not Rely on Pressure in the UST to Stop Flow – allowing    faster fill times and reducing spill risk.
  • Speeds Delivery Operations – product flows unimpeded into the tank    until the hose “kick” that accompanies the valve shut-off provides a clear signal that the liquid has reached the shut-off level.
  • Simple and Inexpensive Installation – in both two-point and coaxial fill applications, no additional excavation, manholes or vent piping are required.


  • Valve Body: Cast aluminum
  • Float: Nitrile rubber, closed cell foam
  • Valve: Aluminum 
  • Seals: Viton®
  • Upper & lower drop tube: Aluminum  
  • Plastic parts: Acetal
  • Hardware: Stainless steel

Related Products