Definition
The butterfly valve is an important device in the water supply and drainage pipeline system. With the advancement of industrial technology, different requirements are imposed on the structure and performance of the butterfly valve. Therefore, in the design and selection, reasonable choices should be made for its type, materials and connection forms according to working conditions.

Classifications
* Classified by structure
(1) Center sealing butterfly valve
(2) Single eccentric sealing butterfly valve
(3) Double eccentric sealing butterfly valve
(4) Three eccentric sealing butterfly valve

* Classified by sealing surface material
1. Soft sealing butterfly valve:
a) The sealing pair is made of a non-metallic soft material to a non-metallic soft material.
b) The sealing pair is made of a metal hard material to a non-metallic soft material.
2. Metal hard sealing butterfly valve: The sealing pair is composed of a metal hard material and a metal hard material.

*Classified by seal
1. Forced sealing butterfly valve
a) Elastic sealing butterfly valve. The sealing specific pressure is generated by the valve plate pressing the valve seat, the valve seat or the valve plate when the valve is closed.
b) External torque sealing butterfly valve. The seal specific pressure is generated by the torque applied to the valve shaft.
2. Pressure sealing butterfly valve. The seal specific pressure is generated by the compression of the spring seal element on the valve seat or valve plate.
3. Automatic sealing butterfly valve. The seal specific pressure is automatically generated by the medium pressure.

* Classified by work pressure
(1) Vacuum butterfly valve. A butterfly valve with a working pressure lower than that of the standard atmosphere.
(2) Low pressure butterfly valve. Butterfly valve with nominal pressure PN<1.6MPa.
(3) Medium pressure butterfly valve. The nominal pressure PN is a butterfly valve of 2.5--6.4 MPa.
(4) High pressure butterfly valve. The nominal pressure PN is a butterfly valve of 10-80MPa.
(5) Ultra high pressure butterfly valve. Butterfly valve with nominal pressure PN>100MPa.

* Classified by operating temperature
(1) High temperature butterfly valve: T>450 ℃ butterfly valve
(2) Medium temperature butterfly valve. 120 ℃ < T< 450 °C.
(3) Normal temperature butterfly valve. 40℃
(4) Low temperature butterfly valve. 100 ℃< T < 40 ℃.
(E) Ultra-low temperature butterfly valve. T < 100 ℃