Backflow valves are designed to block drainpipes temporarily and prevent flow into the house. They are available in a variety of designs. A "gate" backflow valve provides a strong seal, but must be operated by hand. The effectiveness of a gate valve will depend on how much warning you have of impending flooding.
A "flap" or "check" valve opens to allow flow out of the house but closes when the flow reverses, so the sewer water can't flow back up into the pipes. These valves operate automatically, so the homeowner does not have to be around if flooding occurs, but do not provide as strong a seal as a gate valve.
Points to keep in mind:
- Changes to the plumbing in your house must be done by a licensed plumber or contractor, who will ensure that the work is done correctly and according to all applicable codes. This is important for your safety.
- Some valves incorporate the advantages of both flap and gate valves into a single design. Your plumber or contractor can advise you on the relative advantages and disadvantages of the various types of backflow valves.
- Valves should be installed on all pipes that leave the house or that are connected to equipment that is below the potential flood level. Valves may be needed on washing machine drain lines, laundry sinks, fuel oil lines, rain downspouts and sump pumps, as well as sewer/septic connections.
- If you have a sump pump, it may be connected to underground drain lines, which may be difficult to seal off.