A backwater valve is a device installed in a drainage system to prevent reverse flow. When installed correctly, the valves prevent sewage from re-entering the structure. A backwater valve is not to be confused with a backflow prevention assembly. Backflow prevention assemblies are installed in drinking water supply systems and fall under the jurisdiction of the plumbing code and/or the City Water Code. Search Portland.gov under the subject Backflow to find out more information.
Below are the code sections that cite when you need to install backwater valves.
OPSC Section 710.0: Drainage of Fixtures Located Below the Next Upstream Manhole or Below the Main Sewer Level.
OPSC Section 710.1 Backflow Protection.
Fixtures installed on a floor level that is lower than the next upstream manhole cover of the public or private sewer shall be protected from backflow of sewage by installing an approved type of backwater valve. Fixtures on such floor level that are not below the next upstream manhole cover shall not be required to be protected by a backwater valve. Fixtures on floor levels above such elevation shall not discharge through the backwater valve. Cleanouts for drains that pass through a backwater valve shall be clearly identified with a permanent label stating "water valve downstream".
OPSC 710.6 Backwater Valves.
Backwater valves, gate valves, fullway ball valves, unions, motors, compressors, air tanks, and other mechanical devices required by this section shall be located where they will be accessible for inspection and repair and, unless continuously exposed, shall be enclosed in a masonry pit fitted with an adequately sized removable cover.
Backwater valves shall comply with ASME A112.14.1, and have bodies of cast-iron, plastic, copper alloy, or other approved materials; shall have noncorrosive bearings, seats, and self-aligning discs; and shall be constructed so as to ensure a positive mechanical seal. Such backwater valves shall remain open during periods of low flows to avoid screening of solids and shall not restrict capacities or cause excessive turbulence during peak loads. Unless otherwise listed, valve access covers shall be bolted type with gasket, and each valve shall bear the manufacturer's name cast into the body and the cover.