What is a Force Main System?

I've mentioned in my blogs that Pipeline Pigging can be used to clean Force Main systems, but I don't remember ever explaining just what a force main is.

I referenced the EPA website to get a good explanation of this topic.

Force Main Piping systems carry pressurized wastewater away from a pump or pneumatic ejector toward its discharge point.  The pressurizing equipment is located at a lift station and provide the energy to move the wastewater through the piping system.

A  Force Main System is made up of Pipes, Valves, Pressure Surge Control Devices and Force Main Cleaning Systems.

Force Main Systems can be made from a variety of materials depending on the conditions that are expected inside and around the pipes. They are also constructed of various diameters of pipes. Wastewater quality and composition is the primary determining factor of piping material and desired flow rate is the key to deciding on diameter and wall thickness. Corrosion resistance will be among the variables considered, as will operating pressure and trench conditions.

Some facilities will choose to aerate the wastewater or add chlorine at the lift station to control odors and limit corrosion. Pressure surge control devices help prevent system damage and are especially important during system startup and shut-down. These are usually automatic cone or ball valves.

As I mentioned briefly above and have written about before, Force Main System cleaning is generally accomplished using Inline Pipe Pigging. Pig insertion facilities are usually included in the lift station and a retrieval station is located at the discharge point. Longer Force Main Systems may include multiple insertion / retrieval points throughout their course to allow easier access for cleaning.

When might a Force Main System be needed?

When the discharge point is at a higher elevation than the source of the wastewater, gravity cannot be used. One might seek alternative processing locations at lower elevation, but in locations such as beachfront Florida, there simply isn't any lower ground on which to build a facility.

Use of Force Main Systems can also significantly reduce the size and depth of the trenches, thereby decreasing the overall costs of sewer system construction. Often, gravity sewers must be installed in trenches deeper than twenty feet, pushing the cost of sewer line installation significantly higher due to the complex and costly heavy excavation equipment and
trench maintenance required. The diameter of pressurized force mains is usually one to two
sizes smaller than the diameter of gravity lines, allowing significant pipeline cost reduction. Force main installation can also be simpler because of shallower pipeline trenches and
reduced earthwork. Installation of Force Main System is not dependent on site specific topographic conditions such as available terrain slope, which typically limits gravity wastewater
movement.

Force Main System reliability and useful life are comparable to
that of gravity sewer lines. Pipeline reliability may be compromised by excessive pressure surges,  corrosion, or lack of routine maintenance. Pipeline Pigging for cleaning and inspection should play a significant role in that routine maintenance schedule.