拍门主要安装在排水管道的尾端，用于防止外水倒灌。材质分为不锈钢、铸铁、型钢、复合材料(玻璃钢)等多种材料。
The flapping door is mainly installed at the tail end of the drainage pipe to prevent backfilling of external water. Material is divided into stainless steel, cast iron, section steel, composite materials (FRP) and other materials.
而拍门又分为很多种，比如，浮箱式拍门，平板式拍门，套筒式拍门等等是安装在江河边排水管出口的一种单向阀，当江河潮位高于出水管口，且压力大于管内压力时，拍门面板自动关闭，以防江河潮水倒灌进排水管道内。
There are many kinds of flapping doors, such as floating box flapping doors, flat flapping doors, sleeve flapping doors and so on. They are one-way valves installed at the outlet of river drainage pipes. When the river tide level is higher than the outlet and the pressure is greater than the pressure in the pipe, the panel of flapping doors automatically closes to prevent the river tide from pouring into the drainage pipes