A backwater valve is a plumbing device that prevents the backflow of sewage. The valve helps air flow freely through drain pipes, which allows sewage to flow in the right direction: out of your home. Building codes differ based on your locality, but generally, if your home is located below the first manhole cover on the street’s sewer line, a backwater valve will be required. There is a greater chance of a basement flooding the lower down the street it is located on a sloping sewer line. In some areas, however, installing a backwater valve is mandatory anytime a building is located very close to the first upstream manhole cover.
How does the valve work?
What a backwater valve does is allow sewage to flow in only one direction. Especially in older neighborhoods where sanitary disposal systems are combined with storm drains, a period of heavy rain can strain drainage systems to capacity.
The drainage system is not able to disperse the additional water, and that water will flow back up the lowest opening it can find, usually a floor drain. What a backwater valve does is prevent this from happening. Inside the valve is a circular metal trap that remains open as long as waste is flowing out of the home. The minute wastewater begins to flow backward, however, the trap swings shut. This means that the backwards flowing water will need to find some other available opening because it will not be able to reenter your home.
Since the backwater valve works by swinging shut when necessary, occasionally a piece of debris can prevent the device from functioning correctly, usually something that has been flushed that should not have been. The valve requires regular maintenance, including lubrication and checking that its connections are functioning. This can be done by a certified plumber and it is recommended that homeowners do this once a year. For houses that have a history of flooding due to sewage backflow or houses that are located in neighborhoods with a history of flooding, installing a backwater valve is a wise investment even if your locality does not require it.
