Current situation, application and development of

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The current situation, application and development of valves

infrastructure construction is the focus of China's economic construction. The scale of water supply and drainage projects, especially sewage treatment projects, is huge. The WTO has entered, the western development has been launched, and the valve market has a bright prospect. Although China's tap water industry has a history of nearly 120 years, seven years earlier than Japan, there is still a big gap and needs to be built. The current situation is that half of more than 700 cities in China are short of water, and 100 cities are seriously short of water. The average annual water consumption will increase by 7million m3/D; In particular, during the Ninth Five Year Plan period, it was proposed that the operators who first used the equipment should be instructed by skilled operators. One of the keys to the treatment of environmental pollution is sewage treatment, focusing on the treatment of three lakes (Taihu Lake, Chaohu Lake and Dianchi Lake) and three rivers (Huaihai River, Liaohe River and Haihe River). At the same time, 640 county-level cities with a population of more than 500000 were required to build at least one sewage treatment plant in one city by 2003, During the Ninth Five Year Plan period, the sewage treatment rate is 25%, and it is required to reach 46% in 2010, that is, 1000 plants. At present, there are only sewage treatment plants in more than 200 prefecture level cities nationwide, and sewage treatment plants will be built in nearly 400 cities in the next few years. By 2003, 180billion yuan will be invested to treat urban sewage. Since 2000, 60billion yuan will be invested every year, and the annual equipment investment will reach 20billion yuan. Valves also account for a large share. A medium-sized sewage treatment plant needs about million yuan of valve investment. In addition, the demand of water supply engineering, hydropower, chemical industry and other industries is also large. By 2008, Beijing will invest 180 billion yuan to host the Olympic Games, most of which will be used in capital construction, and the number of valves used in capital construction will also be considerable. The above situation is only the domestic market. After entering the WTO, the domestic market we can see is only a small piece, and the larger market is abroad. Now it has entered globalization. We should make full use of the advantages of China's valve industry and actively move towards the platform of the world economy. The design, production status, application and development of valves in China are briefly described in several topics. 1. Current situation after the reform and opening up, with the vigorous development of China's economic construction, the valve industry has also shown a thriving vitality. At present, there are thousands of large and small valve factories. Although the good and bad are mixed, the product varieties have reached more than 3000 models and nearly 30000 specifications. Great progress has been made in sealing performance, strength requirements, regulating function, action performance and circulation performance, especially sealing performance. Ten years back, an authoritative person of the urban water supply association has an industry famous saying, "ten valves and nine leaks", although it is exaggerated, it is really not desirable. For example, from September to December 1989, Chengdu water supply company inspected 145 valves, with a pass rate of 72.5%. In 1996, 917 valves were inspected, with a pass rate of 88.66%. Due to the limitation of inspection methods, they cannot be accepted according to national standards. If they are strictly in accordance with national standards, the pass rate will be lower. Gate valves mainly have poor sealing performance, butterfly valves and operating mechanisms have poor reliability. This situation has indeed been significantly improved. Now the ductile iron casting process, resin sand casting process Many manufacturers have mastered the technical and material problems of austenitic stainless steel valve shaft, hard seal valve seat, special valve varieties, application of anti-corrosion coating, and seal structure design. Some (a few) manufacturers' products have approached and reached the international advanced level. They have used high-end epoxy resin Araldite for an 18 month research project to replace imported products, or exported abroad, and the overall level is also constantly improving, The distance with foreign advanced level is further narrowed. However, the overall level of China's machinery manufacturing industry is not high, so the quality of valves needs to be further improved. 2 commonly used valves in cities, buildings, enterprises and fixtures, the size of the experimental force they can bear is a very important indicator of fixtures. In water supply and drainage projects, medium and low pressure valves are widely used, especially low-pressure large-diameter valves (low-pressure valves refer to valves with nominal pressure PN ≤ 1.6Mpa) can be used as furniture, ceilings, etc., while medium pressure valves (pn2..4mpa) are few, According to the principle and structure classification (international common method), the commonly used valves are butterfly valves and gate valves, and the others are ball valves, check valves, exhaust valves, plug valves, diaphragm valves, pressure reducing valves, flow regulating valves, sludge discharge valves, etc. 2.1 current situation and development of gate valves gate valves have been used for the longest time and are still used in countries all over the world, especially below dn300mm, and still play a leading role in all kinds of valves. According to the shape of the valve plate, it is divided into parallel gate valve and wedge gate valve. Wedge gate valve is widely used internationally. Its characteristic is that the pressure difference between the front and rear of the valve plate forces the valve plate to press on the valve seat on the outlet side, which has good sealing performance. When it is fully opened, the pressure loss is small because the valve plate does not stay in the flow path. Used to cut off the medium in the pipeline. Its disadvantage is that the operating torque is large, and it is easy to damage the valve body and stem during operation, especially the large mouth gate valve. The overall size and weight are also large. The DN1000 caliber gate valve is about 3200mm high and requires four people to operate, so the gate valve is generally suitable for small caliber, that is, below DN500. The flow resistance of the gate valve is small from full opening to middle opening. When it is close to full closing, the flow resistance increases sharply. In a large range, the change of flow resistance is small. When it is close to full closing, the flow changes greatly. It must not be used when the valve is close to closing. At this time, it is difficult to fine tune the flow. If the opening of the valve is very small and the flow rate at the opening is very fast, cavitation will occur at the lower side of the ram, accompanied by intense vibration noise. Long time throttling operation will often cause cavitation of the metal of the valve body and the ram. If the working condition of the gate valve is in the middle opening, the valve plate is supported by the guide rails on both sides, so it fits closely when it is fully closed. When it is in the middle position, the gap between the valve plate and the guide rail is large, causing vibration. Therefore, even in areas with low cavitation incidence, if the valve is throttled for a long time, the guide rail will be deformed, worn or damaged, and because the valve seat is not in full contact, and the surface pressure of the contact part is very high, biting or adhesion will often occur. Therefore

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