Plastic check valves offer this security with very simple devices. The valve body is a cylindrical piece that is molded, extruded, or die cast and installed midway in the piping.

These non-return valves are simple to install in existing pipeline layouts since they do not require any external activation or actuation mechanisms. The body supports a ring-shaped plastic device known as the seat. This stretches from the inner walls to the pipe's centerline, although it does not completely shut.

A plugging device, such as a piston or ball, is located in the seat. A swinging disk is another type of plugging device. When pressure is sufficient and moving in the desired direction, the stopper is pulled away from the seat of the valve, opening the the gap to allow process stream to flow freely down.