in order to prevent sediment deposition block valve opens, the lower edge of the butterfly valve reverse current closed, hydrodynamic torque M always tend to close the valve. The hydrodynamic pressure on the valve component of P moving along the flow direction, and move upward along the direction vertical component P1. When the valve is closed, perfectly still, water under hydrostatic pressure of the valve. Because of the valve position different from top to bottom, hydrostatic action center below the center line of valve. Therefore, for horizontal axis butterfly valve, will produce lead to hydrostatic torque rotary valve. In the operation of the valve, the operating mechanism of every rotary pin shaft friction force and friction moment. Among them, the valve between the shaft and bearing friction force and torque is the primary value for the most part of total friction torque. According to the design conditions, valve shaft and the friction coefficient of aluminum bronze is equal to zero. 15, therefore, when the maximum water head of 121. 5 m, according to its own weight automatically closing butterfly valve, does not automatically shut down the phenomenon of the necessary conditions for mu> 0. 2. 7. As a result, can draw the following conclusions: ( 1) Butterfly valve operation after more than two years, many sands may occur between valve shaft and bearing, lead to valve shaft and bearing clearance is reduced, the bearing friction coefficient increased. In the process of valve closing, when the valve is close to the seated position, pressure difference between fluctuation two parts of the valve. The differential pressure will produce a block valve shaft closed moment. The drag torque is proportional to the friction coefficient of bearing. When the torque is greater than the moment when the valve is closed, can appear the phenomenon. ( 2) Run after a period of time, the bearing lubrication surface may corrode, bearing wear and friction coefficient increase, can also lead to the above phenomenon. 4 processing method ( 1) Change the closing butterfly valve operating procedure. Close the butterfly valve, open the bypass valve. After close the valve, close the bypass valve again. In this way, after the closing of the butterfly valve can balance the water pressure, eliminate closing butterfly valve upstream and downstream pressure differential, greatly reduce the frictional resistance of closed smoothly closing process, reduce the wear of bearing lubrication. Reduced the surface, improve the service life of the bearing of butterfly valve. ( 2) Two hammer side reserved four (screw hole. Some steel plates can be added to the hammer, then screwed. This will increase the weight of the hydraulic hammer, thereby increasing the weight of the butterfly valve closing torque, so that the bearing friction coefficient increases, the butterfly valve can be closed smoothly. In the above two methods, if use the second method, modified butterfly valve can be closed for a period of time, but after a long run, with the valve shaft and bearing between the deposition of sediment and further wear for bearing lubrication, and the cause of more and more with the increase of the coefficient of friction. Frictional resistance is big, the butterfly valve may not close on its own, even need to be replaced. Bearings. Therefore, considering the problem of processing difficulty and the safe and economic operation in power plants, adopt the method of modified butterfly valve closing process.

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