Gravity Return-Line Design: Why Installation Cost and Space Matter
When a stage-3 vapor recovery unit recovers liquid fuel, that fuel must flow back into the underground tank. It sounds trivial, but the height of the return line determines whether the installation needs civil work — and that can mean the difference between a one-day installation and a construction project.
The problem with low return lines
In many stage-3 units on the market, the inlet, return and vent connections are located at the bottom of the cabinet, roughly 30–50 mm above ground. Recovered liquid has to be pushed uphill into the tank, or has to rely on a very shallow gravity slope through a pipe that is nearly at ground level. In practice, this does not work reliably without assistance. The typical fix is to raise the whole unit on a platform 500–550 mm high so that gravity can do the work. That platform is civil work: concrete, steel, time and money, and often an obstruction in an already tight tank-farm layout.
The gravity return-line design
The WHSH-M places the inlet, return and vent connections at mid-height — about 500–550 mm above ground. The recovered liquid therefore has a natural gravity head over the tank’s inlet, and flows back by gravity alone. No return pump is needed, and no raised platform is needed.
What this means in practice
– Installation: the unit is set on a level concrete pad (recommended 2000 × 2000 × 200 mm), piping is connected, and the unit is ready. Installation is normally completed in one day.
– Piping: the inlet line is DN50; the return line is DN20, fitted with a shut-off valve and a check valve to prevent backflow.
– Civil work: none beyond the standard equipment pad. Stations with an existing pad can often place the unit directly.
– Reliability: gravity flow has no pump to fail, no pump seals to leak, and no power draw. It also handles the recovered liquid gently, with no emulsification from pumping.
– Maintenance: the return line stays clear because the flow is continuous and unobstructed; checking it is part of the monthly inspection routine.
What to ask a supplier
When comparing stage-3 units, ask two questions:
1. What is the height of the return connection above ground?
2. Does the installation require a raised platform or additional civil work?
The answers affect both the initial cost and the footprint of the system. A unit with a mid-height gravity return line installs faster, costs less to install, and occupies less space — an advantage that matters at existing stations where the tank-farm area is already crowded.
For more information: +86 135 2699 0215 / lixiang@vohonoilpipe.com
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