 | | (Figure 1) Flap (Check) Valve - Example of an Automatic Valve. The simple flap valve, also called a check valve, is the most-popular and least-expensive backflow valve. Since the flap is normally closed, it must be pushed open by sewer water. Solids in the sewage may stick on the seal, causing the valve to fail. Check valves are available at home improvement stores. |
 | | (Figure 3) Ball Valve - Example of a Manual Valve. The ball valve is open when the handle is in line with the sewer line. The valve is fully closed by turning the handle a quarter-turn so it is perpendicular to the sewer line. |
 | | (Figure 5) Gate Valve - Example of Manual Valve. The gate is open when the gate is "up." The valve is closed using multiple clockwise turns of the handle, resembling a typical outdoor water faucet. |
|  | | (Figure 2) Hydraulic Flap Valve - Example of an Automatic Valve. This clear-port flap valve offers the advantage of being normally open (so it doesn't trap solids) and closing with force when the sewer system floods. The valve can be submerged, can be fitted with a by-pass pump and comes in residential and municipal sizes. |
 | | (Figure 4) Hydraulic Gate Valve - Example of Automatic Valve. This clear-port gate valve offers the advantage of being normally open (so it doesn't trap solids) and closing with force when the sewer system floods. Since the valve may not work if the canister is submerged, it should be used in basements or on the dry side of floodwalls and levees. |
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