Force Main

Published: | Updated: November 20, 2020

Definition - What does Force Main mean?

A force main is a pressurized sewer pipe that conveys wastewater under pressure from the discharge side of the pump. Force mains are used where gravity is not enough to move sewage or stormwater runoff through a sewer line. Pumps or compressors are used to push the sewage through the force main from a lower to a higher elevation or across landscapes where deep excavation is not feasible.

Force mains are installed in lifting stations and are fitted with pumps that help convey the wastewater to a higher elevation. They act as support systems for wastewater sewer lines that are installed in low lying areas that require pumping to convey sewage forward to treatment plants that are situated at a higher elevation.

Trenchlesspedia explains Force Main

Force main refers to allsanitary sewer lines that operate using force derived from pumps or compressors that help keep the wastewater moving through them. Usually, the optimal force in a sewer drainage system is gravity. As wastewater moves from homes or buildings into the sewer network, gravity lines require no additional power systems to make the sewage flow. Lateral lines and service connections feed the wastewater into larger municipal sewer pipes and convey it to the wastewater treatment plant.

Need for Force Mains

Gravity lines don’t work in situations where the main sewer line is higher in elevation than the service connections. Moving the wastewater uphill from the service connections to the main lines will require a pump. In such cases, pumping or lifting stations are installed in sewer systems that help keep the sewage flowing.Since force mains use pumps rather than gravity, their alignments can vary by several feet sideways or up and down between access points or pump stations.

In some cases, force mains are also installed in places where deep excavation to install sewer lines is not possible or is too expensive. In such cases, the main sewer lines to receive the flow of the wastewater may actually be lower, but the obstacles for excavation might be too great. Under these circumstances, conducting the flow with pressurized force mains may be the best answer. In some places, the terrain does not support the construction of gravity sewers all the way to the treatment plant.

Maintenance of Force Mains

The main parts of a force main are pipes, valves, pressure surge control devices, and a force main cleaning system. Force mains have to be frequently cleaned and maintained to remove the buildup of grease and solids. The dissolved oxygen in the wastewater gets depleted in the wet well of the lift station. Its subsequent passage through the force main results in wastewater devoid of oxygen and containing sulfides that encourage corrosion

The force main is made from different materials like ductile iron, polyvinyl chloride (PVC), and polyethylene (PE) depending on flow characteristics and quality of wastewater. Ductile iron is preferred due to its high strength, high flow capacity, and tight joints.For corrosive wastewater and high-flow characteristics, polyethylene-lined ductile iron pipes and fittings are preferred. Force mains are reliable and have a long service life if the system is routinely maintained and cleaned.

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