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2011-11-10 03:14:46 Introduction of the Butterfly Valves'Development and Application

The disadvantage of the rubber sealed butterfly valve is that when it's used for cutting down the stream, the rubber seat will peel and be damaged due to the improper use. Therefore, the metal sealed butterfly valve has been developed in the international community. The cavitation area decreases. In the recent years, Japan has also developed the comb-shaped butterfly valve with the features of resistance to cavitation erosion, low vibration and low noise.

Under normal circumstance, the life of rubber sealed seat is 15-20 years and 80-90 years for metal. But how to choose the right requirements will have to keep to the working conditions.

The relationship between the opening rate and the flowing rate is essentially linear. If it’s used to control the flowing rate, the flowing characteristics and the piping of the flow resistance are also closely related. Although install two pipelines with same valve diameter, same form, the flowing rate will be very different if the pipe’s loss coefficient is different.

If the throttle extent is in the state of big margin, the back of the valve plate will be prone to cavitation and there is the possibility of damage to the valve. Generally,it’s used for15 centigrade.

When the butterfly valve is in the middle opening, the valve shaft will be as the center for the valve body and the shape of the openings formed in the front of valve plate. Two sides are used to complete the formation of different states. The side of the front of the valve plate is direct to the moving water, the other side is of the direction of the counter—current water. Therefore, the side of the valve vody and the valve plate may form a nozzle-shaped openings, the other side is similar to the orifice-shaped openings. The flowing velocity on he nozzle side is much faster than that on the cutting side, while the negative pressure will be produced on the side of the throttle valve and this will make the rubber sealed seat off.

The operation torque of the butterfly valve is different due to the different direction of valve opening and closing. Especially for the large- diameter valve, the torque generated by the differences between the two sides of the valve shaft in different water depth can not be ignored. In addition, when the device of the valves on the entry side bends, partial flowing formed and then the torque will increase. When the valve opens in a middle state, the flowing of water causes the torque work. Then the operating devices need to self-lock.


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