Backwater valves are a plumbing device that prevent waste water from backing up into homes. Clogs and backup can still occur from problems inside the home itself, because these devices are intended to protect against outside problems.
All houses on a block will connect together into a single, and much larger, sewer line after leaving the properties. In the unlikely event that this sewer main pipe were to clog, any houses upstream are at risk of flooding with waste water as homes drain sinks, tubs, toilets, and more. It’s especially important for split-level homes, homes with basements, or generally where the sewer line is not significantly lower than the lowest drain in a home or where pipes are not sloped at the perfect angle.
Backwater valves, also known as sewer backflow valves or sewer backup valves, should be installed at the lowest point in the home’s drainage system around the point where it exits through the foundation wall. They are installed so that there is an access panel for when repairs or replacement is necessary. As with most devices, there is a limited life expectancy. Anyone familiar with pool skimmers will recognize how they work. A buoyant flapper sits in the drum area that lets water flow over and past it. If water stops inside the backwater valve drum, the buoyant flapper raises up and seals the unit shut. Water from the street sewer line would build up, and apply pressure to maintain the seal until water is drained out. At this time, no water in the drum means that the flapper drops to its default position and water on the home’s side of pipes can flow freely outward again. Some manufacturers recommend service and cleaning annually, and life expectancies vary by model. Retrofitting a valve is possible, just a little more expensive due to the demolition process to get to the sewer line after foundations and structures are created. Replacing or repairing an existing model is much less expensive, as no demolition should be necessary.
Too Long, Didn't Read Version: Backwater valves keep your home’s drain lines from backing up due to problems on the public utility level, but do not protect from problems inside the home’s drain system.
-Marshall Tramp, CPI, RMP
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