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  Infrastructure construction is the focus of our country's economic construction. The water supply and drainage projects, especially the large-scale sewage treatment projects, have formed a strong aquaculture industry, including pipelines and valves. For the valve industry, provides a good opportunity. China has entered the WTO, the global annual demand of about 3 million tons of valves. To take full advantage of the valve industry is labor-intensive, poor working conditions, low wages in China, developed countries to production transfer in developing countries and other advantages, and actively toward the world economy platform. A few topics to describe the status of the drainage valve and development.

  The current situation 

  There are about 3,000 valve factories in size now, of which 600 are in Wenzhou, nearly 200 in Zhengzhou, more than 150 in Shanghai, 250 in Liaoning, more than 200 in Jiangsu and Fujian. Despite the mixed results, the product variety has reached more than 3,000 models , Nearly 30,000 specifications. In many varieties, sealing performance, strength requirements, regulatory function, performance and flow performance, especially the sealing performance, have made great strides, back ten years ago, authorities of urban water supply industry, there is a saying in the industry that "ten valves Nine leaks ", although some exaggerated, but it is true.
Many problems that cause the valve industry are mainly the rapid expansion of the market after the reform and opening up, and the original state-owned valve enterprises have shut down and turn, the level of the machinery industry was not high, so the township enterprises (private enterprises) are springing up rapidly , The starting point is low, the technical strength is very weak, crude equipment, most of the products are imitation of production, coupled with market turmoil, especially for low pressure valves for drainage, the problem is serious. The past decade, driven by a small number of valve companies, indeed significant progress, some species even reached the international advanced level, there are many companies undertaking the second. But on the whole, the gap is still huge and there is a lot of work to be done. To this end, respectively, made in 2010 and 2020, technological progress, development planning has a very important significance.

  Commonly used valves

  In the water supply and drainage projects, the low pressure valve is widely used, especially low-pressure large-diameter valve (low pressure valve is the nominal pressure PN ≤ 1.6MPa valve), and medium-pressure valve (PN2.5-6.4MPa) less. The valve, butterfly valve is the most basic and most widely used leading product.

  Gate valve status and development

  Gate valve has the longest history, so far the world is still in use, especially DN300mm, in all types of valves is still dominant. The utility model is characterized in that the pressure difference before and after the valve plate causes the valve plate to be forcedly pressed on the valve seat on the right side of the outlet and the sealing property is good and the valve plate does not remain on the flow path when the valve is fully opened Rank the top three, disdain for peer loss. Used to cut the media in the pipe.

  The disadvantage is the large operating torque, easy to make the valve body, stem damage, especially large-diameter gate valve. Dimensions and weight are also large, DN1000 diameter gate valve about 3200mm high, requires four people to manipulate, so the valve is generally used in a small diameter, that DN500 the following.

  Gate valve from the open to the middle of the opening, the valve flow resistance is small, close to fully closed, the sharp increase in flow resistance. In the larger range, the change of flow resistance is smaller. When the flow is close to fully closed, the flow rate changes greatly. Do not use it when the valve is close to the seal. In this case, it is very difficult to fine-tune the flow rate. If the valve opening is extremely small, the flow velocity at the opening is very fast, cavitation will occur on the underside of the gate, and accompanied by intense vibration and noise, long time throttling operation, often make the valve body and gate metal Cavitation.

  If the gate valve operating conditions in the middle of the opening, the valve plate is supported by the guide rails on both sides, fully closed with the close, and the middle position, the valve plate and the guide rail gap and produce vibration. Therefore, the guide rail is deformed, worn or damaged even if the valve is throttled for a long time even in a region where the incidence of cavitation is low, and the pressure at the surface of the contact portion is high because the seat is not in full contact with the surface of the contact portion Bite or adhesion, therefore, should not be used for flow control. Also note that the gate valve in a small opening, the flow changes, if the valve emergency opening and closing, will result in a sharp increase in pressure or negative pressure, especially when the water hammer off the valve.