Rising Main Calculator — Pipe Size, Friction Head & Pump Duty

A rising main is a pressurised pipe that carries pumped effluent or water uphill from a pumping station to a gravity sewer or discharge point. Unlike gravity drains, rising mains flow under pressure and can go uphill. They are typically 50-110mm MDPE or ductile iron pipe.

For a foul rising main, design for a minimum self-cleansing velocity of 0.75 m/s (Sewerage Sector Guidance Appendix C / Sewers for Adoption) so solids do not settle and block the pipe. Keep the velocity below about 1.8 m/s to limit friction losses and water-hammer risk on pump stop. Velocity is calculated on the pipe BORE, not the nominal outside diameter — a 63mm MDPE pipe has an internal bore of roughly 51mm. Select a pipe diameter that gives a velocity within the 0.75–1.8 m/s band at the design flow.

A non-return valve (also called a check valve) is always required on a rising main to prevent backflow when the pump stops. Without an NRV, the sewage in the rising main would flow back into the pump chamber. It is installed on the rising main immediately after the pump discharge.

This calculator uses the Hazen-Williams equation in SI form: hf = 10.67 × L × Q^1.852 / (C^1.852 × d^4.87), where L is the equivalent pipe length (m), Q is flow (m³/s), d is the internal bore (m) and C is the roughness coefficient (about 150 for MDPE/uPVC, 130 for ductile iron). Friction loss rises steeply with flow (roughly with flow squared), so it must be worked out at the actual design flow rather than read from a single fixed rate. Bends, valves and fittings add equivalent length — typically 1.5m per bend. The result is added to static head for total pump head. Use our Pump Station Calculator to size the pump based on total dynamic head and flow rate.

MDPE (Medium Density Polyethylene) is the standard choice for domestic and small commercial rising mains. It is flexible, corrosion-resistant and easy to join. Ductile iron is used for larger installations or where the pipe passes under roads. uPVC can be used but is less flexible.