Butterfly valve is mainly composed of valve body, butterfly plate, stem, sealing ring and transmission device.
(1) Valve body
The body is cylindrical, and the upper and lower parts have a cylindrical boss for mounting the stem. Butterfly valve and pipe are connected by flange; If the clamp connection is used, its structural length is minimum.
(2) Valve stem
The valve stem is the rotating shaft of the butterfly plate. And the shaft end adopts the packing box sealing structure to prevent the leakage of the medium. The upper end of the valve stem is directly connected with the transmission device to transfer torque.
(3) Butterfly plate
The butterfly plate is the opening and closing part of the butterfly valve.
According to the connection type can be divided into flange connection and clamping connection; According to the transmission mode can be divided into manual, gear transmission, pneumatic, hydraulic and electric several.
Butterfly valve flow characteristics:
The relationship between the opening of butterfly valve and the flow rate is basically linear proportional change. If it is used to control the flow, its flow characteristics are also closely related to the flow resistance of the pipe. For example, the two pipes are installed with the same valve diameter and form. And the pipeline loss coefficient is different. And the flow of the valve will be very different. If the valve is in a large throttle range state, the back of the valve plate is prone to cavitation. There is the possibility of damage to the valve, generally used at 15°.
When the butterfly valve is in the middle opening. The valve body and the front end of the butterfly plate form the opening shape with the valve shaft as the center. The two sides form different states, one side of the front end of the butterfly plate moves in the direction of the flow water. The other side moves in the direction of the countercurrent water. Therefore, one side of the valve body and the valve plate form a nozzle-shaped opening, the other side is similar to the throttle hole opening, the nozzle side is much faster than the throttle side flow rate. The throttle side of the valve under the negative pressure, often appear rubber seals fall off.
Butterfly valve operating torque, due to the opening degree and the valve opening and closing direction of the different values are different. Horizontal butterfly valve, especially large diameter valve, due to the water depth, the valve shaft, water head torque generated by the difference can not be ignored. In addition, when the inlet side of the valve is installed with the elbow. The deflection will be formed and the torque will be increased. When the valve is in the middle opening. The operating mechanism needs to be self-locking due to the action of water flow torque.