Infrastructure is the focus of China's economic construction, drainage works, especially the sewage treatment works in size manufacturing water treatment equipment including pipes, valves, has formed a strong water industry. For the valve industry, provides a good opportunity. China has entered the WTO, the global annual demand valve about 3000000 tons. To take full advantage of the valve industry is labor-intensive, poor working conditions, low wages per capita, the developed countries to developing countries to shift production and other advantages, and actively to the world economic system. Several topics outlined to the present situation and development of drainage valve, hydraulic control valve.

     problems exist in the valve industry is mainly after the reform and opening up, the market rapidly expanded, and the original state-owned enterprises have Guantingbingzhuan valve, had mechanical industrial level is not high, so the township and village enterprises (private enterprises), like bamboo shoots after a spring rain has developed rapidly, the low starting point, the technical force is very weak, poorly equipped, most products are produced to imitate, coupled with the confusion in the market, especially with the drainage of low-

     pressure valve, a serious problem. In the past ten years, in a small number of enterprises valve drive, there was progress, and some species even reached the international advanced level, there are many enterprises do poineering work the two times. But on the whole, the gap is still very great, a lot of work to do. To this end, respectively 2010, 2020 technical progress, development planning has very important significance.

Common valve

      In water supply and drainage engineering, is widely used in low pressure valve, special low-voltage large-diameter valves (low pressure valve is the valve nominal pressure PN ≤ 1.6MPa), and the medium pressure valve (PN2.56.4MPa) less. The gate valve, butterfly valve is the dominant product is the most fundamental and most widely used.

Present status and development of 2.1 valve

     Valve using the oldest, has the world's countries are still used, especially DN300mm the following, still occupies a leading position in various types of valves in the. The valve plate is characterized by pressure before and after valve plate to force the pressure in the outlet on the right side of seat, seal better, and fully open, the valve plate does not stay in the flow on the road, because the pressure? China building material - building a bit? Ranked the top three, disdain for peer loss. Used to cut off the pipeline medium.

     The disadvantage is the operating torque, operation is easy to make the valve body, valve stem damage, particularly in large diameter valve. Dimensions and weight are also great, DN1000 valve diameter of about 3200mm high, you need four operations, the valve usually used in small caliber, that is use the following DN500.

     Valve from fully open to the middle opening, the valve flow resistance small, close to the fully closed, the flow resistance increased dramatically. A large range, small changes in flow resistance, close to the fully closed, the flow changes in large, close off the valve must not use, then fine-tuning is difficult to flow. If the valve opening is extremely small, fast opening of the flow rate, the lower side gate will produce cavitation, and accompanied by intense vibration and noise, long time cutting operation, tend to make the body and gate metal cavitation.

       If conditions in the middle gate opening, the valve plate because it is relying on both sides of the rail support, fully closed with the close, while the middle position, the valve plate and the large gap rail vibration. Therefore, even in a low incidence of cavitation region, long time to throttle valve operation, rail defects can occur, wear or damage, and because the seat is not fully exposed, and exposed parts of the surface pressure is high, often will have a bite corrosion or adhesion, therefore, should not be used for flow control. Also note, the valve in the small opening, the flow rate changes, if the valves open and close an emergency, will cause a sharp rise in pressure or negative pressure, especially when the valve off the generation of water hammer.