Butterfly valve overview

A butterfly valve is a valve that uses a circular disc as a starting and closing member and rotates with the valve stem to open, close and adjust the fluid passage. The butterfly valve's disc is mounted in the diameter direction of the pipe. In the cylindrical passage of the butterfly valve body, the disc-shaped disc rotates around the axis, and the rotation angle is between 0° and 90°. When the rotation is 90°, the valve is fully open.
The development history of butterfly valves In the 1930s, the United States invented the butterfly valve. It was introduced to Japan in the 1950s and was widely used in Japan in the 1960s. In China, it was promoted after the 1970s. At present, butterfly valves in the world generally have been replaced by DN300 mm butterfly valves. Compared with the gate valve, the butterfly valve has a short opening and closing time, a small operation, a small installation space and a light weight. Taking DN1000 as an example, the butterfly valve is about 2T, and the gate valve is about 3.5T, and the butterfly valve is easy to combine with various driving devices, and has good durability and reliability. The disadvantage of the rubber sealing butterfly valve is that when it is used for throttling, cavitation may occur due to improper use, and the rubber seat may be peeled off and damaged. To this end, the metal sealing butterfly valve has been developed internationally, and the cavitation zone has been reduced. In recent years, China has also developed a metal sealing butterfly valve. In recent years, a cam-shaped butterfly valve resistant to cavitation, low vibration and low noise has been developed in Japan. 
Generally, the life of the sealing seat is under normal conditions, rubber is 15-20 years, and metal is 80-90 years. However, how to choose correctly depends on the requirements of the working conditions. 
The relationship between the opening of the butterfly valve and the flow rate changes substantially linearly. If it is used to control the flow, its flow characteristics are closely related to the flow resistance of the piping. For example, the diameters and forms of the two pipe installation valves are all the same, and the pipe loss coefficient is different, and the valve flow difference is also large. 
If the valve is in a state of large throttle, the back of the valve plate is prone to cavitation and may damage the valve. Generally, it is used outside of 15°. 
When the butterfly valve is at the middle opening degree, the shape of the opening formed by the valve body and the front end of the butterfly plate is centered on the valve shaft, and the two sides are formed to complete different states. The front end of the butterfly plate moves along the water direction and the Other side flows in the opposite direction. Therefore, one side valve body forms a nozzle-like opening with the valve plate, and the other side is similar to the orifice-shaped opening. The nozzle side has a much faster flow rate than the throttle side, and the negative pressure is generated under the throttle side valve. A rubber seal will come off. 
The butterfly valve and the butterfly rod have no self-locking capability. For the positioning of the butterfly plate, a worm gear reducer is added to the valve stem. The use of a worm gear reducer not only enables the disc to have a self-locking capability, but also stops the disc at any position and improves the valve's operating performance.
The operating torque of the butterfly valve varies depending on the opening degree and the direction of opening and closing of the valve. Horizontal butterfly valves, especially large-diameter valves, cannot be ignored due to the water depth and the head difference between the valve shaft and the head. In addition, when the valve inlet side device is bent, a bias current is formed and the torque is increased. When the valve is at the intermediate opening, the operating mechanism needs to be self-locking due to the action of the water flow torque.

The butterfly valve is simple in structure and consists of only a few parts. The material consumption is saved. The volume is small, the weight is light, the installation size is small, the driving torque is small, the operation is simple and rapid, and only 90° rotation can be used to quickly open and close; With good flow regulation and closed sealing characteristics, butterfly valves are the dominant valve type in the field of large and medium diameter, medium and low pressure. When the butterfly valve is in the fully open position, the thickness of the disc is the only resistance when the medium flows through the valve body, so the pressure drop generated by the valve is small, so it has better flow control characteristics. The butterfly valve has two sealing types: a spring seal and a metal seal. Elastomeric sealing valve, the sealing ring can be mounted on the valve body or attached to the periphery of the disc. Valves with metal seals generally have a longer life than elastomeric seals, but are difficult to seal completely. Metal seals can accommodate higher operating temperatures, while elastomeric seals have temperature-limited defects. If a butterfly valve is required for flow control, the main choice is the correct size and type of valve. The structural principle of the butterfly valve is especially suitable for making large diameter valves. Butterfly valves are widely used not only in general industries such as petroleum, gas, chemical, and water treatment, but also in cooling water systems for thermal power plants. Common butterfly valves are clip-on butterfly valves and flanged butterfly valves. The wafer type butterfly valve uses a stud bolt to connect the valve between the two pipe flanges. The flange type butterfly valve has a flange on the valve, and the flanges on both ends of the valve are connected to the pipe flange by bolts. The strength properties of a valve are the ability of the valve to withstand the pressure of the medium. Valves are mechanical products that withstand internal pressure and must therefore have sufficient strength and rigidity to ensure long-term use without cracking or deformation.
With the application of anti-corrosion synthetic rubber and polytetrafluoroethylene, the performance of the butterfly valve is improved and is satisfied by different working conditions. In the past ten years, metal sealing butterfly valves have developed rapidly. With the application of high temperature resistance, low temperature resistance, strong corrosion resistance, strong erosion resistance and high strength alloy materials in butterfly valves, metal sealing butterfly valves are exposed to high temperature, low temperature and strong erosion. It is widely used under various working conditions and partially replaces the globe valve, gate valve and ball valve.

Structural features of the butterfly valve The butterfly valve has the characteristics of simple structure, small volume, light weight, low material consumption, small installation size, rapid switch, 90° reciprocating rotation and small driving torque. It is used for cutting, connecting and adjusting the pipeline. Medium with good fluid control and closed sealing properties.
The butterfly valve can transport the mud and accumulate less liquid at the mouth of the pipe. A good seal can be achieved at low pressure. The adjustment performance is good.
The streamlined design of the disc makes the fluid resistance loss small, which is an energy-saving product.
The valve stem is a through-rod structure. After quenching and tempering treatment, it has good comprehensive mechanical properties, corrosion resistance and scratch resistance. When the butterfly valve is opened and closed, the valve stem only rotates and does not perform lifting operation. The packing of the valve stem is not easy to be broken and the sealing is reliable. It is fixed with the cone pin of the butterfly plate, and the overhanging end is designed to prevent the punch-out type, so as to prevent the valve stem from collapsing when the valve stem and the butterfly plate are accidentally broken.
Connections are flanged, clip-on, butt-welded and lug-to-clip.
The driving form includes manual, worm gear, electric, pneumatic, hydraulic, electro-hydraulic linkage and other actuators, which can realize remote control and automatic operation. The disadvantages of the butterfly valve are as follows:
1. The use pressure and working temperature range are small.
2. Poor sealing.