Drop Tube Cut Calculator

Check each step as you complete it. Do not skip or reorder steps.

• Confirm actual tank capacity from the calibration chart. Verify it is ACTUAL capacity, not nominal. ⚠ Nominal and actual capacities can differ significantly. Never use nameplate volume.
• Install the Face Seal Adaptor (FSA) and Spill Container on the fill riser per OPW instructions.
• Measure Dimension A using the 71SO measuring stick — top of FSA threads to inside top lip of tank (hook in lengthwise direction). Mark the stick just below the drain valve outlet, at the top of the FSA threads.
• Measure Dimension B — same FSA reference point to bottom of tank.
• Inspect the riser pipe: clear all burrs, relining overspray, obstructions, or internal weld beads. Confirm Schedule 40 pipe. 🚫 DO NOT install in Schedule 80 pipe — the 71SO is designed for Schedule 40 ONLY.
• Verify 14" minimum clearance from center of fill riser to any obstruction in all directions. 🚫 If clearance < 14", the valve float may not operate correctly.
• If ball float vent valve is present: confirm 71SO shutoff occurs BEFORE the ball float restricts delivery flow. See OPW Figure 24.
• Enter all measurements into calculator, select drill tool, press Calculate. Verify results before making any cuts.
• Mark the upper tube cut length from the seam where the upper tube meets the valve body. Complete the calculation above to see cut length.
• Attach supplied band clamp just below the cut mark as a square-cut guide.
• Cut upper tube SQUARE with a hacksaw (fine-tooth — 24 teeth/inch). Rotate tube while cutting to maintain squareness. 🚫 NEVER use a pipe cutter or tubing cutter — it deforms the tube and prevents assembly.
• File the cut end square and remove ALL burrs and sharp edges. File a chamfer on the INSIDE edge of the tube.
• Sand inside of tube with fine-grit sandpaper or steel wool. Wipe the inside clean for the top ~4 inches with a clean rag. ⚠ Failure to chamfer, sand, and clean may cut the polypak seal and cause the valve to fail a pressure decay test.
• Apply black moly grease completely around the inside diameter of the upper drop tube.
• Confirm polypak seal lip is facing UP on the inlet tube. Apply black moly grease all around the polypak seal. 🚫 If polypak seal lip is facing down, the valve will leak vapor. Lip MUST face up.
• Slide inlet tube into upper tube until upper tube bottoms against the flange. Polypak seal must stay seated in its groove.
• Install drill tool over the inlet tube and align the key slot. Complete tool selection above to see tool-specific instructions.
• Verify drill stop dimension before drilling. Complete tool selection above to see stop dimension.
• Drill three (3) 3/16" holes through the UPPER TUBE ONLY using the drill tool as a guide. 🚫 If the drill penetrates the inlet tube or enters a screw hole — the assembly is NOT salvageable. Stop and obtain replacement parts.
• Remove the drill tool. Dimple all three (3) holes with a punch and hammer until the tube deforms into the countersunk hole in the inlet tube. Remove tool before dimpling. Clear metal chips from screw holes after each punch.
• Apply black moly grease to all three screws. Install the three supplied taptite #10-24 screws so they are flush with the outer tube surface. ⚠ Torque: 20 in-lbs minimum · 35 in-lbs maximum. Use ONLY the supplied taptite screws — no substitutions.
• Apply black moly grease to the lower o-ring and valve body threads. Install o-ring in groove above the threads.
• Thread lower tube onto valve body until it bottoms out. Hand-tight, or use a strap wrench on the threaded insert only.
• Mark lower tube cut length from the underside of the inlet tube flange. Complete the calculation above to see cut length.
• Cut lower tube at the calculated length. Cut at 45° or per local code. File off any sharp burrs. 🚫 Use hacksaw only (24 TPI fine tooth). Remove ALL chips from cut end before insertion.
• Optional — pre-insertion pressure test: seal valve with inflatable plumber's plugs; max 10" W.C. (approx. 1/3 PSI). If valve leaks, do not install — contact OPW warranty.
• Thoroughly clean the top of the riser pipe. Final inspection — no obstructions, no debris.
• Remove elastic band from the float NOW — just before insertion. Not before. ⚠ Removing the elastic band too early may cause float damage.
• Confirm upper O-ring/gasket is under the inlet tube flange. Hold float down and slowly lower valve into riser — do not drop or force. 🚫 If resistance is felt at any point, STOP. Clear the riser pipe. Do not force the valve past an obstruction.
• Align float along the length of the tank (not across). Verify orientation using other manholes or pump boxes. ⚠ Float must be aligned along tank length or shutoff behavior will be affected.
• Install Jack Screw Kit and 4" NPT nipple to lock valve in position. Valve must NOT rotate while tightening. Verify float alignment is maintained.
• Install Rotatable Product Adaptor per OPW instructions.
• Install warning plate approximately 1" below the adaptor on the riser. Secure with supplied cable tie.
• If an electronic tank monitor (ATG) is installed: calibrate it so that the top of the 71SO valve body equals 95% of actual tank capacity. Do not calibrate to 100% — 100% tank capacity reference for the ATG should be the top of the 71SO valve body.
• Leave the OPW installation instructions (H15524PA) with the station operator for their records.
• Save or print this install record.