Pressure Sewer and Small-Bore Wastewater Systems

About this course.

A pressure sewer, also called a small-bore or low-pressure sewerage system, is a way of collecting and transporting wastewater in which each connected property has its own small pump station — a buried collection tank fitted with a grinder pump — that macerates the incoming wastewater and pumps it under pressure through small-diameter mains to the wider sewer or treatment system. The essential difference from a conventional gravity sewer is that a gravity sewer relies on the natural fall of the land to carry wastewater downhill in large, partly filled pipes, whereas a pressure sewer supplies the energy mechanically at each property, so it can push wastewater along and even uphill through much smaller, fully charged pipes that follow the ground.

To understand why this matters, it helps to picture how a gravity sewer behaves. In a gravity system, wastewater flows because the pipe is laid at a continuous downward gradient, and the pipe runs only part full so that air can move above the flow. Maintaining that gradient across a whole area dictates how deep the pipes must be. On flat or undulating ground, keeping a constant fall over long distances forces the pipes progressively deeper, which means deep trenching, and often pumping stations to lift the flow back up so the gradient can begin again. Gravity systems also use access structures such as maintenance holes at junctions and changes of direction. All of this is proven and robust, but it is excavation-intensive and depends on having usable fall.