August 2021 Vol.76 No. 8
Features
Five Steps to a Successful Sewer Bypass Project
By Neil Ripley, Regional Product Development Manager for United Rentals Fluid Solutions
Sewer overflows are a daily occurrence. Clearing, repairing or replacing a pipe usually requires a temporary sewer bypass to divert the discharge from point A to point B and create a work area.
Every sewer bypass project has potential pitfalls. However, careful planning, installation and monitoring can reduce the risks of spills and leakages. For any company designing, installing and operating a sewer bypass, following these five important steps can make project success more likely.
Protect people, environment
Worker safety and environmental safety always need to be at the top of the mind with any bypass operation. That means companies need to follow confined space protocols. Anyone working in a confined space, such as a sewer, should be properly trained, equipped and supervised.
During sewer bypass setups and teardowns, workers may be exposed to raw influent wastewater that can carry bloodborne pathogens. Encourage the worksite team to have hepatitis A and B shots to help protect themselves.
Use a spill containment berm at the worksite. That includes placing a berm under equipment, positioning it to capture any fuel, oil or wastewater.
Size the bypass system right
Companies need to determine the maximum anticipated flow and design of the bypass system, including addressing any site-specific challenges. A good first step is to create a professional drawing to conceptualize the bypass system for a particular project site, and how the system will address project needs and constraints. This is an area where a professional fluid solutions provider can have a major impact on project success.
Sound attenuated, diesel-driven centrifugal pumps are the typical choice for the standard sewer bypass. However, if the suction lift is too great, submersibles or benching may be required.
Typically, in sizing the system, the total dynamic suction lift should be no greater than 25 feet. This measurement is taken from the surface of the water (at its lowest operating level) to the eye of the pump impeller. The measurement also needs to take into consideration site elevation (for NPSHa purposes), as well.
The typical recommended submergence depth is 6 feet. However, in certain applications, both the suction lift and liquid depth parameters may vary. A suction lift that is too high or too low can cause performance loss or equipment damage. Also, design your system so the suction velocity does not exceed 10 feet per second. To avoid potentially rupturing, flattening or causing flow surging inside the discharge line, make sure the system is evacuating air with strategically placed air release valves.
For the purposes of safety, a job site should have – 100 percent of the time – backup pumps plumbed in and at the ready in case of mechanical failure of the primary pumping system. If repair onsite isn’t feasible, project teams should make it easy to swap pumps in and out as needed. In set up, teams need to create good access points for situations such as fueling and preventative maintenance.
Keep the bypass running smoothly
Here are a few tips that can help ensure a bypass system operates properly.
Every project should be monitored by an experienced, capable worker watching the system 24/7, checking suction manhole depths at a minimum of 15-minute intervals. To complement pump watch personnel, a telemetry system can be installed to automatically send alerts for problems involving fuel level, oil pressure, coolant temperature, flow rate, suction and discharge pressure, and more.
During times when the temperature will dip below freezing, be sure to consider ways to keep the pumping area warm. When less than 32 F degrees, water that isn’t moving (such as running a system using on/off floats) will freeze, and can crack the volute in the pump and destroy it. This can cause costly damage and, more importantly, disrupt the bypass. Use space heaters, electric blankets or tents, as needed to help prevent freezing.
Check and test before startup
Fixing system performance issues becomes much more complex once a bypass system goes live. Here are some ways to help reduce the risk of developing system issues.
Even though each pump may have been inspected by a qualified mechanic, it never hurts to re-check all pump wet end, and engine lubricant and fuel levels before activating a bypass system. Additionally, apply a vacuum plate to the suction side of the pump to test for proper vacuum. After a pump leaves the shop and is delivered to a worksite, it may sit for days, weeks or more before being ready to run. It is sound practice to conduct some basic checks one last time before installation.
Outfit the suction system with a vacuum gauge on the priming and suction side and a pressure gauge on the discharge side for continuous monitoring of system performance and troubleshooting, if needed.
Be sure to test the telemetry system if the project is using one. Make sure the system is connected and that all sensors are sending signals. Another important step before startup is to test the discharge pipe/hose for leaks by filling it with fresh water before pumping sewage.
Before every startup, make sure to affix to each pump set an emergency contact list, and be sure onsite personnel know where to find the plan. This list could include an emergency environmental response company, the nearest hospital location, and other people you would want onsite immediately in the event of an emergency.
Follow teardown, removal procedures
When the job is finished and it is time to tear down the temporary bypass, do it the proper way. Remove the plug at the lowest flow times. This is generally between 11 p.m. and 4 a.m.
Keep the equipment in ready position. If the owner’s system isn’t ready to accept the flow, the worksite team may need to restart the pumps to avoid serious spills.
Be sure to sanitize and disassemble the system. When the owner’s system is back up and running, make sure all equipment is properly sanitized and disinfected with clean water and bleach or sodium hypochlorite. Of course, properly dispose of the cleaning water.
As a best practice, consult an expert before beginning a sewer bypass project and ensure personnel are wearing the proper PPE.
For more information, visit unitedrentals.com.
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