Operator terms · Wastewater
What is a force main?
A force main is a pressurized sewer pipe that carries wastewater pumped from a lift station up to a higher point or on to the plant. Unlike a gravity sewer, it flows full and under pressure because a pump, not gravity, moves the water.
Last reviewed 2026-08-03
How it differs from a gravity sewer
A gravity sewer runs partly full and downhill on its own. A force main runs full and under pressure because a lift station pump pushes the wastewater through it, often uphill, to where gravity flow can resume.
What operators watch
Because it is pressurized, a force main break sprays wastewater, and slow spots can let solids and gases build up. Operators watch pump pressure and run times to catch problems on the line.
Common questions
- Is a force main pressurized?
- Yes; a pump pushes wastewater through it under pressure.
- How is it different from a gravity sewer?
- It flows full and under pressure instead of downhill by gravity.
- What feeds a force main?
- A lift station pump moving wastewater from a wet well.