Sewage Pump Outlet Size and Pipe Velocity: A Guide

Buyers often choose the pipe to match the pump outlet without checking the velocity. For sewage, velocity is what decides whether the pipe stays clean.

The velocity window

Keep the velocity in the discharge pipe between about 0.7 and 3 m/s. Below 0.7 m/s, solids settle in the pipe and it slowly blocks. Above 3 m/s, friction losses climb quickly, the pump needs more head, and the pipe wears faster.

Velocity by pipe size

These values are for the nominal pipe bore; the real inside diameter of your pipe changes them slightly.

Flow	DN50	DN65	DN80	DN100	DN150
10 m³/h	1.4 m/s	0.8 m/s	0.6 m/s	0.4 m/s	0.2 m/s
20 m³/h	2.8 m/s	1.7 m/s	1.1 m/s	0.7 m/s	0.3 m/s
40 m³/h	5.7 m/s	3.3 m/s	2.2 m/s	1.4 m/s	0.6 m/s
60 m³/h	8.5 m/s	5.0 m/s	3.3 m/s	2.1 m/s	0.9 m/s
100 m³/h	14.1 m/s	8.4 m/s	5.5 m/s	3.5 m/s	1.6 m/s

Pump outlet versus pipe size

The pump outlet is sized for the pump, often at a higher velocity than you want in a long pipe. For a short discharge, matching the outlet is fine. For a long rising main, it often pays to go one size larger after the pump: the friction loss falls sharply, and the pump may need less head. Just check that the velocity at your minimum flow stays above 0.7 m/s.

Solids passage

Sewage pumps start at DN50 so that solids can pass. If the liquid carries large solids, check the maximum solids size of the pump as well as the outlet size.

Our head calculator shows the pipe velocity and warns you when it is too low or too high.