Butterfly valve open and close is a disc-shaped pieces of butterfly plate in the valve body around its own axis of rotation, so as to achieve open and close or adjust the valve is called butterfly. Butterfly full-to full-off is usually less than 90 degrees, butterfly valves, and butterfly stroke does not have a strong self-locking, in order to butterfly plate positioning, to stem worm reducer to install. Seals can be classified according to the form of soft-and hard-seal sealing two kinds. Soft vented type commonly used rubber ring seal, hard-vented type commonly used metal ring seal.