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.

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  • Features & Benefits
  • Ordering Specifications
  • Replacement Parts
  • Notes & Warnings
  • Downloads


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

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.

Features & Benefits

  • Simple, Easy and Quick Installation – No excavation or special manholes required.
  • Economical – Costs a fraction of expensive, complicated and difficult-to-install valves.
  • Furnished Complete – Supplied with new upper and lower drop tubes, mounting hardware and thorough instructions for quick job site time.
  • Completely Automatic Operation – No pre-checks to perform, no resets, and no overrides to be broken or abused.
  • No Pressurization of the Tank – Operates directly from liquid level.
  • Will Accept a Dipstick for Gauging.
  • Retrofits Directly – For both new and existing tanks with 4" fill risers.
  • Quick Drain Feature – Automatically drains hose when head pressure is relieved.
  • Best Flow Rate in The Industry.*

  • * Test-witnessed by Bowser-Morner, Inc., an independent laboratory. Results available upon request.

No Epoxy Sealants Required!

Raising the Standard in Overfill Prevention

From the company that brought you the industry standard OPW 61SO, OPW raises the standard with the introduction of the New 71SO Overfill Prevention Valve – breakthrough innovation that takes overfill prevention to a whole new level of overfill perfection.

The new 71SO is a two-stage, positive shut-off valve, providing completely automatic operation with no pre-checks to perform, no resets, and no overrides to be broken or abused. The valve closes when the tank level rises to 95% capacity and provides a special bypass valve so the tank can be filled to a maximum capacity of 98%. The 71SO is available for direct-bury and remote applications.

  • Eliminates curing issues due to hot or cold temperatures
  • Easier, quicker, installation
  • Higher quality, more reliable installation
  • Lower costs
  • Greater protection against fugitive emissions and pressure decay
  • Fastest flow rate in the industry

Listings & Certifications

Ordering Specifications

Product No. Description A-Upper Tube Length B-Lower Tube Length C-Overall Length. Max. Riser Length Max. Nominal Tank Dia. Max. Actual Tank Dia. Weight
in. m in. m in. m in. m in. m in. m lbs. kg
71SO-400C Vapor-Tight Overfill Valve, 5 Ft. Bury, 8 Foot Tank 60 1.5 83 2.1 154-3/4 3.9 53-1/2 1.4 96 2.4 107 2.7 16 7
71SO-410C Vapor-Tight Overfill Valve, 10 Ft. Bury, 10 Foot Tank 120 3.1 102 2.6 234-3/4 5.9 113-1/2 2.9 120 3.1 126 3.2 25 11
71SO-420C Vapor-Tight Overfill Valve, 10 Ft. Bury, 12 Foot Tank 120 3.1 126 3.2 258-3/4 6.5 113-1/2 2.9 144 3.7 150 3.8 26 12
71SO-4000 Non Vapor-tight Overfill Valve, 5 ft. Bury, 8 ft. Tank 60 1.5 83 2.1 155-3/4 3.9 53-1/2 1.4 96 2.4 107 2.7 16 7
71SO-4010 Non Vapor-Tight Overfill Valve, 10 Ft. Bury, 10 ft. Tank 120 3.1 102 2.6 234-3/4 5.9 113-1/2 2.9 120 3.1 126 3.2 25 11
71SO-TOOLCT 71SO Installation Tool 2.5 1
61JSK-4RMT Jack Screw Kit for Vapor-Tight Remote Applications 1.5 0.7
61JSK-4410 Jack Screw Kit for Composite Base Spill Buckets 1 0.5
61JSK-44CB Jack Screw Kit for Cast Iron Base Spill Buckets 1 0.5

71SO Instruction Sheet Order Number: H15524PA

Replacement Parts

Product Number Description
61SOK-0001 Replacement Float Kit
H11931M Drop Tube Seal
H14840M Lower Tube Seal

61JSK-4410 and 61JSK-44CB Instruction Sheet Order Number: H15289M

Notes & Warnings

NOTE: The 71SO Overfill Prevention Valve can be adjusted to shutoff at any desired tank capacity. Please contact the Authority Having Jurisdiction (AHJ) and review local, state, and national codes to determine the regulatory requirements governing shut-off capacity in your region, as well as take into account other considerations such as extreme tank tilt. In all cases, the upper tube must protrude into the tank at least 6 1/2" to ensure that the valve can shut off flow into the tank completely before the top of the tank is wetted as per EPA requirements.


In order to prevent product spillage from the Underground Storage Tank (UST), properly maintained delivery equipment and a proper connection at the tight-fill adaptor are essential. Delivery personnel should be managed and trained to inspect delivery elbows and hoses for damaged and missing parts. They should always make certain there is a positive connection between the adaptor and elbow. If delivery equipment is not properly maintained, or the elbow is not securely coupled to the adaptor, a serious spill may result when the OPW 71SO closes, causing a hazard and environmental contamination.

NOTE: The OPW 71SO is designed for use on tight-fill gravity drop applications only. Do not use for pressure fill applications.