So the effectiveness of a gate valve will depend on how much warning you have of impending flooding. Among the simpler valves are a flap or check valves, which open to allow flow out of the house but close when the flow reverses. These valves operate automatically but do not provide as strong a seal as a gate valve. 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. If you have a sump pump, it may be connected to underground drain lines, which may be difficult to seal off. These figures include the cost of excavation and back-filling.