Metal sealed valves generally have longer service life than elastic sealed valves, but it is difficult to achieve complete sealing. The metal seal can adapt to higher working temperature, while the elastic seal has the defect of temperature limitation.???

2. Operating principle of pneumatic butterfly valve switch:
The opening and closing of butterfly valve valve is completely completed by the rotation of hydraulic ring servomotor. The power for the butterfly valve hydraulic ring servomotor is mainly from the oil pressure system, which consists of two pressure oil pumps, oil valves, hydraulic valves, four-way slide valves and oil pipelines. The hydraulic annular servomotor is composed of butterfly valve spindle, annular cylinder body, piston, action arm, split half key, split chamber diaphragm and oil inlet and outlet holes. The butterfly valve valve is integrated with the main shaft, which is connected with the action arm through the split key. Under the action of pressure oil, the piston of the hydraulic ring servomotor moves along the ring cylinder body with the main shaft of the butterfly valve as the rotation center, and then drives the main shaft of the butterfly valve to rotate through the action arm connected with the piston, and the main shaft drives the valve to rotate, so as to achieve the purpose of opening and closing the butterfly valve.
The reason why the hydraulic ring servomotor is selected to operate the butterfly valve during the opening and closing process is that the hydraulic ring servomotor has outstanding advantages: in the fixed shaft rotary transmission, it can overcome the shortcomings of the straight cylinder type servomotor that the action arm in the starting and limiting areas of the transmission becomes shorter and the force is dispersed. However, the relative position between the cylinder body of the ring servomotor and the main shaft of the butterfly valve, that is, the concentricity between the center of the ring cylinder body and the main shaft of the butterfly valve, and the perpendicularity between the central plane of the cylinder body and the main shaft axis of the butterfly valve, are difficult to guarantee during manufacturing, processing and installation.