The current situation
Now there are about 3,000 large and small-sized valve factories, including 600 in Wenzhou, nearly 200 in Zhengzhou, more than 150 in Shanghai, 250 in Liaoning, and more than 200 in Jiangsu and Fujian. Although the products are mixed, there are more than 3,000 types of products. , nearly 30,000 specifications. In the many varieties, sealing performance, strength requirements, adjustment functions, action performance and circulation performance, especially sealing performance, have made great progress, ten years ago, the authoritative person of the town water supply association has an industry famous saying "ten valves Nine Leaks, although somewhat exaggerated, is indeed a fact.
The numerous problems that existed in the valve industry were mainly due to the rapid expansion of the market after the reform and opening up, and the original state-owned valve companies were shut down and switched. The level of the mechanical industry was not high, and township and village enterprises (private enterprises) developed rapidly. , The starting point is low, the technical force is very weak, the equipment is simple, most products are imitating production, coupled with market chaos, especially the low-pressure valve for water supply and drainage, the problem is serious. In the past decade, driven by a small number of valve companies, there have been notable advances. Some varieties have even reached the international advanced level, and many companies have started their second ventures. But on the whole, there is still a big gap and there is a lot of work to be done. Therefore, it is of great significance to make technical progress and development plans for 2010 and 2020 respectively.
Commonly used valves
In the water supply and drainage project, medium and low pressure valves are widely used, especially low-pressure and large-diameter valves (low pressure valves are valves with a nominal pressure of PN ≤ 1.6MPa), and medium pressure valves (PN2.5-6.4MPa) are less. Gate valves and butterfly valves are the most basic and widely used leading products.
2.1 Status and Development of Gate Valves
Gate valves have the longest history of use, and they are still in use in all countries of the world. Especially below DN300mm, they still dominate the various types of valves. It is characterized by the pressure difference between the front and the back of the valve plate to force the valve plate to be forced on the valve seat on the right side of the outlet. The seal is better, and when the valve is fully opened, since the valve plate is not left on the flow path, the pressure is very low. · Ranked top 3, disdain for small losses. Used to cut off the medium in the pipeline.
The disadvantage is that the operating torque is large, and the valve body and the valve stem are easily damaged during operation, especially the large-diameter gate valve. Dimensions and weight are also large, DN1000 caliber gate valve is about 3200mm high, requires four people to operate, so the gate valve is generally used in a small diameter, that is, DN500 below.
Gate valve from full open to the middle opening, the valve flow resistance is small, close to fully closed, the flow resistance increased dramatically. In the larger range, the flow resistance changes little. When the flow is close to full closure, the flow rate changes greatly and must not be used when the valve is closed. It is difficult to fine tune the flow rate at this time. If the opening of the valve is extremely small and the flow rate at the opening is extremely fast, cavitation will be generated at the lower side of the gate, accompanied by intense vibration and noise. The long throttle operation will often cause the valve body and gate metal to occur. Cavitation.
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. When the valve plate is fully closed, the valve plate is tightly fitted. In the intermediate position, the valve plate and the guide rail have a large gap and generate vibration. Therefore, even in areas with low cavitation erosion rates, when the valve is throttled for a long time, the guide rails may be deformed, worn, or damaged. Since the valve seats are not in full contact with each other, the contact surface pressure is high, often resulting in Erosion or adhesion, therefore, should not be used for flow control. Also note that when the gate valve is at a small opening, the flow rate changes greatly. If the valve is opened and closed in an emergency, the pressure will rise sharply or generate negative pressure, especially when the valve is closed.
Current Status of China's Drainage Valve Industry and Its Development Prospects
Infrastructure construction is the focus of China's economic construction. Water supply and drainage works, especially large-scale sewage treatment projects, have formed a strong water industry in the water treatment equipment manufacturing industry, including pipelines and valves. Provide a good opportunity for the development of the valve industry. China has entered the WTO, the global annual demand for about 3 million tons of valves. To make full use of the valve industry is labor-intensive, poor labor conditions, China's low per capita wages, the advantages of developed countries to transfer production to developing countries, and actively go to the platform of the world economy. Several topics briefly describe the status and development of water supply and drainage valves.