Sewer Bypass Pumping for Pipeline Rehabilitation

Sewer Bypass Pumping for Pipeline Rehabilitation

Pipeline rehabilitation is one of the most common and most critical operations in municipal wastewater infrastructure management. Aging sewer mains need to be relined, repaired, and replaced across the country every year. Every one of those projects requires bypass pumping to keep sewage flowing while the work gets done.

Here is what contractors and municipal engineers need to know about sewer bypass pumping for pipeline rehabilitation projects.

What is Pipeline Rehabilitation?

Pipeline rehabilitation refers to the repair, renewal, or replacement of existing sewer mains without full open cut excavation. Common rehabilitation methods include:

Cured in place pipe lining (CIPP) — a resin saturated liner is inserted into the existing pipe and cured in place, creating a new pipe within the old one. One of the most common rehabilitation methods for gravity sewer mains.

Pipe bursting — a bursting head is pulled through the existing pipe, fracturing it outward while simultaneously pulling a new pipe into place. Used for both same size and upsized replacements.

Slip lining — a smaller diameter pipe is inserted into the existing main. Lower cost but reduces pipe capacity.

Spray applied lining — structural or corrosion resistant coatings sprayed onto the interior pipe wall. Used for corrosion protection and minor structural rehabilitation.

Spot repair — localized repair of specific defects identified during CCTV inspection. Less disruptive than full length rehabilitation.

Every one of these methods requires the pipe to be taken out of service during the rehabilitation process. Bypass pumping keeps the flow moving while the pipe is offline.

Why Bypass Pumping is Critical for Rehabilitation Projects

Unlike new construction where a sewer main is being installed for the first time, rehabilitation projects involve taking an active main offline. Sewage is flowing through that pipe right now. It needs to go somewhere while the work is done.

Without bypass pumping sewage backs up into the collection system, overflows manholes, and potentially backs up into homes and businesses upstream of the work zone. The consequences are serious — public health risks, regulatory violations, emergency response costs, and community relations damage.

Bypass pumping is not optional on rehabilitation projects. It is a critical component of every project plan.

Planning Bypass Pumping for a Rehabilitation Project

Successful bypass pumping on a rehabilitation project starts with thorough planning well before mobilization.

Flow data — obtain actual flow monitoring data for the pipe being rehabilitated. Design your bypass system for peak flow — not average flow. Peak flow in a residential sewer main can be 3 to 4 times the average daily flow and typically occurs during morning and evening peak periods.

Bypass route — plan the complete bypass route from the upstream connection point to the downstream discharge point. Identify all obstacles, road crossings, and access constraints along the route. Long bypass runs may require multiple pump stages or larger diameter bypass piping to manage friction losses.

Connection points — identify the upstream manhole where the bypass pump will be installed and the downstream manhole where bypass flow will be discharged. Confirm manhole dimensions to ensure the pump can be lowered in and positioned correctly.

Redundancy — never plan a bypass pumping operation without redundant pump capacity. A bypass pump failure on an active sewer main is an emergency. Have a backup pump staged and ready to deploy in minutes — not hours.

Permits and notifications — bypass pumping operations may require permits from the local sewer authority or regulatory agency. Notify the utility owner and relevant agencies before starting bypass operations.

Sizing the Bypass Pump

Pump sizing for sewer bypass is one of the most critical — and most consequential — engineering decisions on a rehabilitation project.

Calculate peak flow — use flow monitoring data to determine peak flow in the pipe being bypassed. If flow data is not available estimate based on pipe diameter and service area characteristics. When estimating always be conservative — overestimate rather than underestimate.

Calculate total dynamic head — measure the elevation difference between the upstream pump location and the downstream discharge point. Add friction losses for the bypass piping length and diameter. This gives you your operating head pressure.

Select pump for operating conditions — using the pump curve select a pump that delivers your required GPM at your operating TDH. Never select based on maximum GPM rating alone.

Size backup pump for full flow — your backup pump must be capable of handling the full bypass flow on its own. A backup pump sized for partial flow does not protect you if the primary pump fails during peak flow conditions.

Bypass Pump Installation and Setup

Once your pump is selected and on site proper installation is critical for reliable operation.

Lower the pump — submersible sewage pumps are lowered into the upstream manhole using a lifting chain or cable. Position the pump at the proper depth to maintain adequate submergence throughout the operating level range.

Install bypass piping — route bypass piping from the pump discharge to the downstream manhole connection. Size bypass piping for the required flow rate — undersized piping creates back pressure that reduces pump performance.

Test before going live — before isolating the existing main test the bypass system at flow. Confirm the pump is performing to specification and the bypass route is watertight. Identify and correct any issues before the existing main is isolated.

Isolate the existing main — once the bypass system is confirmed operational isolate the existing main at the upstream connection using a plug or inflatable stopper. All flow now routes through the bypass system.

Monitor continuously — throughout the rehabilitation operation monitor bypass system performance. Check pump operation, monitor bypass piping for leaks, and track flow levels in the upstream manhole. Any rise in the upstream manhole level indicates the bypass system is not keeping up with inflow.

Common Bypass Pumping Mistakes on Rehabilitation Projects

Undersizing for peak flow — designing for average flow and getting overwhelmed during morning or evening peaks. Always size for peak.

No backup pump — the single most dangerous mistake. A bypass pump failure without a backup means sewage overflow until replacement equipment arrives. Always have a backup on site.

Inadequate bypass piping — undersized piping creates back pressure that reduces pump performance and can cause the bypass system to fail under peak flow conditions.

Poor connection point selection — a bypass connection in a manhole that is too small for the pump, too deep to access safely, or in a location that creates long awkward bypass routing creates operational problems throughout the project.

Stopping bypass pumping too early — keep bypass pumping running until the rehabilitated pipe is back in service and flow has been successfully restored. Do not stop pumping until the isolation plug has been removed and normal flow confirmed.

How Flowcor Equipment Supports Pipeline Rehabilitation Projects

Flowcor Equipment supplies submersible sewage pumps and bypass pumping equipment to municipal contractors and rehabilitation contractors across the U.S. We understand the unique requirements of bypass pumping for rehabilitation projects and can source pumps sized for your specific flow and head conditions.

Tell us your pipe diameter, estimated peak flow, bypass route length, and project timeline and we will get you equipment recommendations and pricing within 1 business hour.

Submit a quote request at flowcorequipment.com or call us at 610-241-6770.