The butterfly valve opening and closing piece is a disc shaped butterfly plate, which rotates around its own axis in the valve body to achieve opening and closing or adjustment. The butterfly valve is generally less than 900 from fully open to fully closed, and the butterfly valve and the butterfly stem are not self-locking. In order to position the butterfly plate, a worm gear reducer should be installed on the valve stem. The adoption of worm gear reducer can not only make the disc plate have self-locking ability, stop the disc plate at any position, but also improve the operation performance of the valve.

The special industrial butterfly valve is characterized by high temperature resistance, high applicable pressure range, large nominal diameter of the valve, carbon steel valve body, and metal ring instead of rubber ring for the sealing ring of the valve plate. Large high-temperature butterfly valve I is made of steel plate by welding, and is mainly used in the flue gas duct and gas pipeline of high-temperature medium.

（1） Advantages of butterfly valve:
1. The opening and closing are convenient and fast, labor saving, and the fluid resistance is small, which can be operated frequently.
2. Simple structure, small volume and light weight.
3. The mud can be transported with the least liquid accumulated at the pipe mouth.
4. Good sealing can be achieved under low pressure.
5. Good adjustment performance.

（2） Disadvantages of butterfly valve:
1. The operating pressure and temperature range are small.
2. Poor sealing performance.

（3） Installation and maintenance of butterfly valve:
1. During installation, i valve disc shall be stopped at the closed position.
2. The opening position shall be determined according to the rotation angle of the butterfly plate.
3. For butterfly valve with bypass valve, the bypass valve shall be opened before opening.
4. The installation shall be carried out according to the manufacturer's installation instructions. The butterfly valve with large weight shall be provided with a solid foundation.