Working principle of plastic butterfly valve

Plastic butterfly valve originated from the invention of butterfly valve in the United States in the 1930s. Plastic butterfly valve developed in Japan in the 1950s and was generally used in Japan in the 1960s. The promotion of plastic butterfly valve in China is in the 1970s. Plastic butterfly valves are: PVC butterfly valve, UPVC butterfly valve, CPVC butterfly valve, PVDF butterfly valve, PP butterfly valve. In the world, the butterfly valve above DN300 mm has gradually replaced the gate valve. Compared with gate valve, butterfly valve has shorter opening and closing time, smaller operation torque, smaller installation space and lighter weight. Take DN1000 as an example, the butterfly valve is about 2T, while the gate valve is about 3.5t, and the plastic butterfly valve is easy to be combined with various driving devices, with good durability and reliability. The disadvantage of rubber sealed butterfly valve is that when it is used for throttling, the rubber seat will be peeled off and damaged due to improper use. In recent years, China has also developed metal sealed butterfly valves, and in Japan, comb shaped butterfly valves with cavitation resistance, low vibration and low noise have also been developed.

Working principle of plastic butterfly valve:

The relationship between the opening and flow of plastic butterfly valve is basically linear. If it is used to control the flow, its flow characteristics are closely related to the flow resistance of the piping. For example, the caliber and form of the valve installed in the two pipelines are the same, while the flow of the valve will be greatly different if the pipeline loss coefficient is different. 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 plastic 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 the butterfly plate on one side moves in the direction of flowing water, and the other side moves in the direction of flowing water. Therefore, the valve body on one side and the valve plate form nozzle like openings, and the other side is similar to the orifice shaped openings. The flow velocity on the nozzle side is much faster than that on the throttle side, while the flow velocity on the throttle side There will be negative pressure under the valve on the flow side, and the rubber seal will often fall off.

Plastic butterfly valve and butterfly rod have no self-locking ability. In order to locate the butterfly plate, a worm gear reducer should be installed on the valve rod. The worm gear reducer can not only make the butterfly plate have self-locking ability, stop the butterfly plate at any position, but also improve the operation performance of the valve.

The operating torque of plastic butterfly valve varies with the opening and opening direction of the valve. The torque of horizontal butterfly valve, especially large-diameter valve, due to the water depth and the difference between the upper and lower ends of the valve shaft cannot be ignored. In addition, when the elbow is installed at the inlet side of the valve, the bias current will be formed and the torque will be increased. When the valve is in the middle opening, the operating mechanism needs self-locking due to the action of hydrodynamic moment.

The plastic butterfly valve is simple in structure and only consists of a few parts with low material consumption; it is small in volume, light in weight, small in installation size, small in driving torque, simple and quick in operation, and can be opened and closed quickly only by rotating 90 °; it also has good flow regulation function and closing sealing characteristics. In the field of large and medium caliber, medium and low pressure use, butterfly valve is the leading valve form . When the butterfly valve is in the fully open position, the butterfly plate thickness is the only resistance when the medium flows through the valve body, so the pressure drop generated by the valve is very small, so it has better flow control characteristics.

Butterfly valve has two types of seals: elastic seal and metal seal. Elastic sealing valve, sealing ring can be inlaid on the valve body or attached to the periphery of butterfly plate. The service life of the valve with metal seal is generally longer than that of the valve with elastic seal, but it is difficult to achieve complete seal. The metal seal can adapt to the higher working temperature, while the elastic seal has the limitation of temperature.

Development prospect of plastic butterfly valve:

If plastic butterfly valve is required to be used as flow control, the main thing is to correctly select the size and type of valve. The structure principle of plastic butterfly valve is especially suitable for making large caliber valve. Plastic butterfly valve is not only widely used in petroleum, gas, chemical industry, water treatment and other general industries, but also used in the cooling water system of thermal power station. There are two kinds of plastic butterfly valves: wafer butterfly valve and flange butterfly valve. Plastic wafer butterfly valve is connected between two pipe flanges with stud bolts. Flange butterfly valve is equipped with flange on the valve, and the flange on both ends of the valve is connected to the pipe flange with bolts. The strength performance of the valve refers to the ability of the valve to bear the medium pressure. The valve is a mechanical product bearing internal pressure, so it must have enough strength and rigidity to ensure long-term use without fracture or deformation.

With the application of anticorrosive synthetic rubber and polytetrafluoroethylene, the performance of butterfly valve can be improved and meet different working conditions. In recent ten years, the metal seal butterfly valve has developed rapidly. With the application of high temperature, low temperature, strong corrosion, strong erosion and high strength alloy materials in the butterfly valve, the metal seal butterfly valve has been widely used in high temperature, low temperature, strong erosion and other working conditions, and partially replaced the stop valve, gate valve and ball valve.