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The City of Portland, Oregon

Portland, Oregon

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General Information: 503-823-4000


1221 SW 4th Avenue, Room 110, Portland, OR 97204

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Backwater Valves

Backwater Valves

Question: What is a “backwater valve” and under what circumstances should one be installed?

Backwater Valve:  A device installed in a drainage system to prevent reverse flow.

  • When installed and operating in a correct manner, a backwater valve will prevent the reverse flow of sewage or other effluent from re-entering and possibly flooding the dwelling.      

The following code articles describe the criteria and circumstances of when “back water valves” are required.  

OPSC Section:

710.0 Drainage of Fixtures Located Below the Next Upstream Manhole or Below the Main Sewer Level. 

710.1 Backflow Protection. Where a fixture is installed on a floor level that is lower than the next upstream manhole cover of the public or private sewer serving such drainage piping, shall be protected from backflow of sewage by installing an approved type of 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 label, sign or markings, stating water valve downstream". 

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 have bodies of cast-iron, plastic, brass, 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.