Structural characteristics and working principle of butterfly valves

Butterfly valve is a type of valve that uses a circular butterfly plate as the opening and closing element and rotates with the valve stem to open, close, and regulate the fluid channel. There are many types of butterfly valves with a wide range of applications, and they are also the longest type of valve we see on pipelines in our daily lives. This article introduces the structural characteristics and working principle of butterfly valves to you.

Structural characteristics of butterfly valves

Butterfly valves have the characteristics of simple structure, small volume, light weight, low material consumption, small installation size, fast switching, 90 ° reciprocating rotation, and small driving torque. They are used to cut off, connect, and regulate the flow of media in pipelines, and have good fluid control characteristics and closing sealing performance.

The streamlined design of the butterfly valve plate reduces fluid resistance loss.

The valve stem of a butterfly valve is a through rod structure, which has undergone quenching and tempering treatment, and has good comprehensive mechanical properties, corrosion resistance, and scratch resistance. When the butterfly valve is opened and closed, the valve stem only rotates without lifting, and the packing of the valve stem is not easily damaged, ensuring reliable sealing.

The connection methods of butterfly valves include flange connection, clamp connection, welding connection, and lug clamp connection. The driving forms include manual, worm gear transmission, electric, pneumatic, hydraulic, electro-hydraulic linkage and other execution mechanisms, which can achieve remote control and automated operation.

Structural characteristics and working principle of butterfly valves

Working principle of butterfly valve

Butterfly valve is a valve that uses a circular butterfly plate as the opening and closing component to open, close, and regulate the flow of medium in the pipeline. In the cylindrical channel of the butterfly valve body, the circular butterfly plate rotates around the axis, with a rotation angle between 0 ° and 90 °. When rotated to 90 °, the butterfly valve is in a fully open state.

The relationship between the opening of a butterfly valve and its flow rate is basically linearly proportional. If used to control flow, its flow characteristics are closely related to the flow resistance of the piping. For example, if two pipelines are installed with the same valve diameter and form, but the pipeline loss coefficient is different, the difference in valve flow will also be significant.

If the valve is in a large throttling range, the back of the valve plate is prone to cavitation, which may damage the valve. Generally, it is used outside 15 °.

When the butterfly valve is in the middle opening, the opening shape formed by the valve body and the front end of the butterfly plate is centered on the valve shaft, and different states are formed on both sides. The front end of one side of the butterfly plate moves in the direction of water flow, while the other side moves in the direction of water flow. Therefore, one side of the valve body and the valve plate form a nozzle shaped opening, while the other side forms a throttle hole shaped opening. The nozzle side has a much faster flow rate than the throttle side, and negative pressure will be generated below the throttle side valve, Rubber seals often come off.

The operating torque of butterfly valves varies due to different opening degrees and valve opening and closing directions. For horizontal butterfly valves, especially large-diameter valves, the torque generated by the water depth and the difference between the valve shaft and the water head cannot be ignored. In addition, when the elbow is installed on the inlet side of the valve, there will be a deviation flow and an increase in torque. When the valve is in the middle opening position, the operating mechanism needs to be self-locking due to the action of water flow torque.

When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body, so the pressure drop generated through the valve is very small, so it has good flow control characteristics.