Butterfly valve ( English: butterfly valve ) refers to the closing member ( valve flap or disc for disc ), around the valve axis of rotation to achieve the open and close a valve, in the pipeline mainly as shut off and throttling effect. Butterfly valve opening and closing piece is a disc-shaped butterfly plate, in the valve body around its own axis of rotation, so as to achieve the purpose of opening and closing or regulation. Butterfly valve full-to full-clearance is usually less than 90°, butterfly and butterfly pole itself without self-locking ability, in order to butterfly plate localization, in stem with a worm reducer. The use of worm gear reducer, not only can make the butterfly plate with self-locking ability, make the butterfly plate stop at any position, but also to improve the valve performance. Special butterfly features of industrial high temperature, discharge pressure is higher, the valve nominal diameter, the body uses of carbon steel, valve plate sealing ring adopts a metal ring instead of rubber ring. Large high temperature butterfly valve uses the steel plate welding manufacturing, mainly used for high temperature smoke of air and gas medium pipeline.
In 30, the United States invented butterfly valve,50 time pass into Japan, to 60 time only in Japan used generally, but in China it is 70 time later. The world in general DN300mm above has gradually replaced the gate valve butterfly valve. Compared to a gate valve opening and closing time is short, small operation torque, installation space is small and light weight. In the case of DN1000, the butterfly valve and gate valve of about 2T, about 3.5T, and the butterfly valve is easy and various driving device combination, has good durability and reliability.
Rubber sealing butterfly valve for throttling drawback is that when in use, as improper use will produce cavitation, the rubber seat spalling, damage from happening. To this end, it has developed the international metal sealing butterfly valve, cavitation area decreases, in recent years China has also developed a metal seal butterfly valve, in Japan in recent years has developed cavitation resistance, low vibration, low noise of the comb-shaped butterfly.
General seal seat of life in normal circumstances, the rubber15 years -20 years, metal80 years -90 years. But how to choose the right according to the requirements of working conditions.
Butterfly valve opening and the relationship between the flow rate, basically is linear proportional change. If used to control the flow rate, the flow characteristics and piping flow resistance are closely related, such as the two installation of pipeline valve diameter, form, all the same, and the pipe loss coefficient is different, the flow valves difference will be great.
If the valve is in the larger state of throttle valve plate, the back is easy to damage the valve cavitation occurs, may, generally at 15 °external use.
Butterfly valve in the opening, the valve body and the butterfly plate is formed at the front end of the opening shape to the valve shaft as the center, on both sides of the formation of different state, side of the butterfly plate front along the flow direction and the flow direction, the other side reverse move, therefore, side valve body and the valve plate forms a similar nozzle shape opening, the other side is similar to the orifice the U-shaped opening, side of the nozzle side flow more quickly than the throttle, throttle valve and side below can generate negative pressure, often can appear rubber seal off.
Butterfly valve operating torque, because the opening and the valve opening and closing direction different from its value varies, horizontal butterfly valve, especially for large diameter valve, because the water depth, valve shaft, water head difference generated by the torque can not be ignored. In addition, the valve inlet side device bend, forming a bias current, torque will increase. Valves are at a middle opening, due to hydrodynamic moment function, operation mechanism need self-locking.
