The flange plug valve uses a plug body with a through hole as the opening and closing part of the valve. The plug body rotates with the valve stem to achieve opening and closing action. A small plug valve without packing is also known as a "cock". The plug body of the plug valve is mostly a conical body (also known as a cylinder), which forms a sealing pair in conjunction with the conical hole surface of the valve body.

Plug valve is a type of valve that has been used for a long time, with simple structure, fast opening and closing, and low fluid resistance. Ordinary plug valves rely on direct contact between the precision machined metal plug body and the valve body to seal, resulting in poor sealing performance, high opening and closing force, and easy wear. They are usually only suitable for low pressure (not higher than 1 MPa) and small diameter (less than 100 mm) applications.