In the 1930s, the butterfly valve
was invented in United States. It was introduced into Japan in the 1950s and was not widely used until the 1960s. The butterfly valve
was promoted in China in the 1970s. At present, the butterfly valve with DN300 has gradually replaced the gate valve in the world. Compared with the gate valve, the butterfly valve has the advantages of short opening and closing time, light weight, small operating torques and small installation space. Take the butterfly valve with DN1000 as an example. The weight of the butterfly valve with DN1000 is about 2 tons, while that of the gate valve with DN1000 is about 3.5 tons. Although the butterfly valve
has the good performance of wear resistance and reliability, one obvious shortcoming of the rubber seal butterfly valve which is used for throttling is that cavitation may occur due to improper use, causing the pealing off, damage, etc. of the rubber valve seat.
In recent years, many countries, including China, have developed the metal sealed butterfly valve
which has a small cavitation area, and Japan has developed the anti-cavitation valve, the low vibration valve and the low noise comb-shaped butterfly valve.
Under normal circumstances, the service life of the general rubber sealing valve seat is about 15 to 20 years, and that of the metal sealing valve seat is about 80 to 90 years. The proper choice of sealing seat should base on the specific working conditions. The relationship between the opening degree and the flow rate of the butterfly valve
is linearly proportional. If the butterfly valve is used to control the flow, its flow characteristics is also closely related to the pipes' flow resistance. For example, if diameters and types of two pipes to be installed are the same and loss coefficients of them are different, the flow of the two butterfly valves
will also be greatly different. If flow of the valve is large, the back of the valve plate will be prone to cavitation, which may further cause damage to the valve.
When the butterfly valve
is half opened, the opening shape of the valve body and the front end of the butterfly plate is centered on the valve shaft, and the two sides are formed in different states. One side of the butterfly plate moves in the downstream direction, and the other side moves in the upstream drection. Therefore, one opening is nozzle-like and the other opening is throttle-orifice-like. The fluids flow faster on the nozzle-like opening side than that on the throttle-orifice-like opening side. In addition, the negative pressure usually occur on the throttle-orifice-like opening side, which will cause the peeling off of the rubber butterfly valve
. The operating torques of the butterfly valves are different due to the variety of the opening degree as well as the opening and closing direction. The torques resulting from the factors such as the horizontal butterfly valves' depth of water, especially those valves with large diameters valve, can not be ignored. In addition, if inlet sides of valves are equipped with elbows, bias flow will form and torques will become large. When the butterfly valves are half opened, their operating mechanisms need to be self locked due to the torque of water flowing.