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Infrastructure construction is the key point of the economic construction of our country, water and drainage projects, especially the sewage treatment project the huge scale of the water treatment equipment manufacturing including pipes, valves has formed a powerful water industry. It provides a good opportunity for the development of valve industry. Our country already entered WTO, global annual demand valve about 3 million tons. We should make full use of the valve industry which is labor-intensive, poor labor conditions, low wages per capita, the transfer of production from developed countries to developing countries, and actively move towards a platform of the world economy. Divide several questions briefly the status quo and development of water supply and drainage valve.
Current situation
Now there are about 3000 large and small valve factories, including 600 in Wenzhou, nearly 200 in Zhengzhou, more than 150 in Shanghai, 250 in Liaoning, more than 200 in Jiangsu and Fujian, although the good and bad are different, but the product varieties have reached more than 3000 models, nearly 30,000 specifications. In a variety of varieties, sealing performance, strength requirements, adjustment function, action performance and flow performance, especially sealing performance, have made considerable progress, backward ten years ago, the authority of the town water supply association has a famous saying that "ten valves and nine leaks", although some exaggeration, but it is a fact. Many problems caused by the valve industry is mainly after the reform and opening up, the rapid expansion of the market, and the original state-owned valve enterprises have shut down and turn, originally the level of mechanical industry is not high, so township enterprises (private enterprises), mushroomed up rapidly, the starting point is low, the technical force is very weak, simple equipment, most products are imitation production, In addition to the market confusion, especially for water supply and drainage of low-pressure valves, serious problems. In the past ten years, driven by a few valve enterprises, there has been obvious progress, some varieties even reach the international advanced level, and many enterprises to start a second business. But overall, the gap is wide and there is a lot of work to be done. Therefore, it is of great significance to make plans for technological progress and development in 2010 and 2020 respectively.
Common valve
In water supply and drainage engineering, medium and low pressure valves are widely used, especially the low pressure large diameter valve (low pressure valve refers to the nominal pressure PN≤1.6MPa valve), while the medium pressure valve (PN2.5-6.4MPa) is less. And gate valve, butterfly valve is the most basic and most widely used leading products.
The present situation and development of gate valve
Gate valve has the longest use history, so far it is still used in the world, especially DN300mm below, in all kinds of valves is still dominant. It is characterized by the differential pressure of the valve plate before and after the valve plate forced pressure on the valve seat on the right side of the outlet, better sealing, and fully opened, because the valve plate does not stay in the flow path, the pressure loss is small. Used to cut off the medium in the pipeline.
Its disadvantage is that the operating torque is large, easy to damage the valve body and stem during operation, especially the large diameter gate valve. The size and weight of the gate valve is also large. The gate valve of DN1000 caliber is about 3200mm high and needs four people to operate, so the gate valve is generally used in small caliber, that is, under DN500.
Gate valve from fully open to the middle of the opening, the flow resistance of the valve is small, close to fully closed, the flow resistance increases sharply. In a large range, the change of flow resistance is small. When the valve is close to full closure, the flow changes greatly. It must not be used when the valve is close to closing, and it is difficult to fine-tune the flow. If the valve opening degree is very small, the flow rate at the opening is very fast, it will cause cavitation on the lower side of the gate, accompanied by intense vibration and noise. Long time throttle operation will often cause cavitation on the valve body and the gold of the gate. If the gate valve is in the middle opening, the valve plate is closely matched with the guide rail on both sides because it is supported by the fully closed position, and the gap between the valve plate and the guide rail is large and produces vibration in the middle position. Therefore, even in areas with low incidence of cavitation, the valve is operated for a long time, the guide rail will be deformed, wear or damage, and because the valve seat is not in full contact, and the contact part surface pressure is high, often produces bite or adhesion, therefore, it is not suitable for flow control. Also note that when the gate valve is small, the flow rate changes greatly. If the valve is opened and closed urgently, the pressure will rise sharply or produce negative pressure, especially when the valve is closed, the water hammer will be produced.
On the basis of metal seal gate valve, rubber soft seal gate valve has been developed in recent years. Its characteristics are:
(1) There is no concave place at the bottom of the body, and the fluid is in a straight line through the section, which is not easy to accumulate and include foreign bodies.
(2) The gate sealing surface is pressed on the valve body to stop the water, and the closing torque is small.
(3) The sealing performance will not be affected by the bending and stretching of the piping.
(4) The whole valve plate is lined with rubber, corrosion resistance, no rust water.
(5) The valve can be fully opened at the same time to replace the sealing material and O-ring.
(6) Good interchangeability of RAMS.
Due to superior function, the international (especially in Europe) demand increases rapidly, soft seal gate valve was invented 30 years ago in Austria, the annual production of more than 500,000 units in Europe, almost 100% use, is a hard seal gate valve replacement products, its manufacturing caliber in Europe and Japan for DN500, the United States generally used DN400, and Italy can produce to DN1200. But there are also shortcomings, soft seal gate valve is sealed by compression of the rubber seat, whether it is not good to judge, to avoid closing the valve too tight, do not exceed the valve closing torque (torque given in the standard).
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