Vapor return piping lives or dies by its slope. In Stage II systems, gasoline vapor must flow back to the storage tank by gravity, and every sag along the run collects liquid that throttles the path.
Why Sag Points Matter
A low spot fills with condensed fuel over months of operation. Once liquid pools, vapor flow area shrinks and the dispenser’s vapor-to-liquid ratio drifts out of range. Stations then chase balance problems that actually started as a plumbing issue.
Planning the Grade Around Obstacles
Conduits, footings and drainage lines rarely cooperate with a straight slope. Walk the route before installation and decide where the line will rise over an obstacle and where it must fall back. Rises need venting considerations, since a high point can trap vapor pockets during commissioning tests.
Setting and Verifying Slope
Bench the trench bottom to the planned grade and use graded bedding rather than shims under the pipe. Verify with a line level or laser at several points, especially mid-span between supports. After pressure testing but before backfill, one more slope check catches shifts from testing pressure.
Documentation
Record the slope readings at marked stations. When a balance issue appears years later, the as-built slope data tells the troubleshooter whether to look at hardware or at a sag that has developed through settlement.
Working with Existing Dispenser Pads
Retrofits often route vapor lines under existing pads. Keep the grade continuous through these crossings and note the deepest point; this is where future repairs will start digging, and knowing it shortens diagnostic time considerably.