Pros and Cons of Installing Dual Force Mains at Lift Stations
Authors:
- Brian Porter, P.E., Chris Belk, P.E., and Alexandra Jones, P.E. - Hazen and Sawyer
Many municipalities struggle with the selection of an appropriate line size for the range of flows that will be experienced over the design life of a lift station. Managing the wide spectrum of flows into a lift station can make maintaining appropriate scouring velocities in a force main challenging. In cases where dual force mains are warranted, municipalities must also decide whether to install the second force main initially or to delay the installation to a future phase.
The objective of this paper is to outline the pros and cons of installing dual force mains and to present design considerations for a dual force main installation. The paper will also discuss the pros and cons of installing both force mains initially versus installation of the second force main in a future phase.
Installation of dual force mains at a regional lift station has a number of benefits including:
• Efficient and Flexible Pump Management (Operational flexibility)
• Elimination or minimizing the frequency of pigging or cleaning the force main
• System Redundancy
Installation of both force mains during the first phase of construction can be advantageous because it provides the benefits listed above when the pump station is commissioned, and avoids a future disturbance to the environment and to landowners along and in the vicinity of the force main route. Installing both lines in the same phase also assures the line will not be impacted by future development and avoids the potential for damaging the existing pipeline during installation of the second line.
Capital costs, operational costs, and risks must be carefully evaluated and compared prior to deciding whether to install a single force main or dual force mains, and if dual force mains are selected these same factors must be considered to see if both force mains should be installed in a single phase.
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