1? The function of the valve in the water supply pipe network Water supply pipe network will be sent to the tap water distribution to tens of thousands of households, so the distribution network in every corner of the city, the water supply pipe network as few as hundreds of pipe length Km, up to thousands of kilometers. The irreplaceability of water and the necessity of people's existence determine the importance of safe operation of water supply network. However, due to many subjective and objective reasons, the pipeline often has some faults, and the pipe network always needs to be constantly updated and rebuilt. The water users often have to increase or decrease accordingly. Therefore, the phenomenon of water stoppage in local pipe sections is unavoidable. In order to reduce the scope of no-go water, it is necessary to properly install the control valve in the pipe network. Therefore, in an urban water supply network, the number of valves is tens of thousands, and irregularly distributed in the city streets below. Valve is a kind of "keeping a thousand days for temporary" control equipment, usually require the valve to open in place to reduce the water loss of pipe. Once needed, the valve should be able to close quickly and flow reliably. Valve integrity, related to the valve selection, valve manufacturing, piping design, valve assembly, valve opening and closing operations and valve management, of course, the most important reason is the quality of the valve. 2? Study of the problem Through the investigation of the use of 20 valve companies in the pipe network, through the inspection of the ten valve manufacturers, I realized that the valve has a large role in the water supply network, the number of large, widely distributed, a lot of problems. Valve operation in the water supply network is not frequent, long-term standby, once summoned, difficult to work. Therefore, in the valve selection, valve manufacturing, valve inspection, valve assembly, valve management, there are many things worth discussing. 2.1 Valve Selection (1) gate valve and butterfly valve in the water supply pipe network in order to reduce the depth of pipe overburden, the larger pipe size matching butterfly valve, the impact on the depth of the soil is not large, and strive to matching gate valve, caused by the caliber of the dividing line Should be based on specific circumstances to be considered. For nearly ten years of use, the butterfly valve has a higher failure than the gate valve, so expanding the use of the gate valve is noteworthy given the conditions permit. (2) gate valve In recent years, many domestic valve manufacturers, research and development, imitation soft seal gate valve, gate valve than the traditional wedge or parallel double gate valve has the following characteristics: a. Soft seal gate valve body, valve cover Using precision casting casting, a molding, the basic non-machining, do not use sealed copper ring, saving non-ferrous metals. b. soft seal gate valve at the bottom of pits, no accumulation of slag, valve gate opening and closing failure rate is low. c. Soft sealing rubber lined valve plate uniform, interchangeable. Therefore, the soft seal gate valve will be the water industry is willing to adopt a form. At present, the soft-sealed gate valve made in China has a caliber of 1500mm, but most manufacturers manufacture the caliber of 80-300mm. There are still many problems in the domestic manufacturing process. From the circumstances of the inspection, the valve body of a valve manufacturing company in Shanghai is entrusted Domestic foundry resin sand mold casting, soft seal valve plate is imported from a foreign company. The company believes that the key component of the soft seal gate valve is Lined plastic valve plate, and Lined plastic valve plate higher technical requirements, not all foreign manufacturers can achieve, often from the reliable factory purchase assembly. Domestic soft seal gate valve copper nut block is embedded in the liner rubber valve plate above, similar to the structure of the valve, the activity of the nut block friction easy to strip valve liner rubber stripping. A foreign company's soft seal gate valve, copper nut block is embedded in lining rubber gate, forming a whole, to overcome the above shortcomings, but the valve cover and valve combination of high concentricity requirements. When opening and closing soft seal gate valve, do not close the dead, as long as the water stop effect can be achieved, or not easy to open or rubber stripping. A valve manufacturing company in Shandong, the valve pressure test, the use of torque wrench to control the degree of closure, as the water company's valve operators should be more imitation of this hoist method. (3) the current butterfly valve butterfly valve selection of several issues of concern: a. The midline butterfly valve butterfly valve in the use of small diameter butterfly valve in China is very large, the effect is better. There are two major differences in the manufacturing method: a valve lining layer after the support frame (represented by the Tanggu products); there is no support frame after a rubber lining (represented by Zhengzhou products). The former rubber less volume, the latter flow area larger. Some people suspect the latter valve life is short, but according to the survey is not the case. b. Comparison of vertical and horizontal butterfly valve In large and medium-sized butterfly valve, vertical and horizontal valve shaft there is the difference, usually vertical butterfly valve casing deep, water debris easily wound shaft end, opening and closing affect; Butterfly valve gearbox in the side, valve wells in the road to occupy a wide plane, affecting the arrangement of other pipelines. Therefore, the use of medium diameter butterfly valve with more vertical, large diameter butterfly valve in horizontal position under the conditions of horizontal. Regardless of vertical or horizontal, valve opening and closing indicators should take measures to observe from the ground. c. eccentric butterfly valve closing off the middle of the butterfly valve, essentially a squeeze rubber seal seal, especially squeezed near the valve shaft is larger, so the valve life is affected, the valve opening and closing torque is too large. In order to alleviate the shortcomings in this aspect, one-dimensional, two-dimensional and three-dimensional eccentric butterfly valves are designed. The developed three-dimensional eccentric butterfly valve has a sealed state in theory and has been developed by many manufacturers. Tianjin A factory's products using computer-controlled machine tool processing, the products close to the technical requirements in this area. Eccentric butterfly valve bearing water pressure is directional, especially the three-dimensional partial butterfly valve reverse bearing capacity is weak. As the pipe network is ring-shaped, the requirements of the valve to withstand the pressure is the same two-way, so when ordering should emphasize this requirement. d. Soft seal and metal seal Most of the butterfly valves used in the water supply industry are soft-sealed butterfly valves. The following problems occur during the use of the seal: ①Poor rubber quality, easy aging, long-term compression deformation and extrusion cracking; ② Valve In the manufacturing process, it is difficult to ensure that the disc in the body cavity concentricity, often over-squeeze to solve the sealing problem, thus affecting the service life of the valve; ③ vertical butterfly valve shaft and sleeve machining accuracy and only Push the way out of alignment, leading to disc shaking and sagging, forming a leakage; ④ butterfly valve in the construction of the rubber ring damage, affecting the sealing. Some manufacturers for the above problems were the following improvements: ①rubber ring sentinel outside the production, to strengthen the quality control, usually for the water supply industry valves, the choice of EPDM rubber and NBR rubber and natural rubber is not forbidden Blending and reclaimed rubber; ② a factory in Hubei Hubei Province, the entire board on the sealing plate gasket into a short swallowtail tail assembly connection to regulate the pressure of the various parts of the pressure plate to balance the life of the butterfly valve, but this adjustment skills Difficult to master; ③ Tianjin and Shanghai launched a number of individual plant butterfly valve and flange butterfly valve, their sealant ring mounted in the dovetail groove, there is a certain amount of allowance, the butterfly valve can be adjusted to close the squeeze the rubber ring ; ④ a company in Henan Province introduced a "fluorine plastic" ring instead of a rubber ring to improve the wear resistance of the ring and anti-aging; ⑤ many manufacturers to introduce metal seal butterfly valve instead of rubber ring seal butterfly valve. Metal seal butterfly valve seal due to the smaller elasticity, the general use of eccentric structure, especially with three-dimensional eccentric structure is ideal. Metal seal butterfly valve was originally used for high-pressure steam pipe, the price is more expensive, it is not easy to damage the sealing surface in operation, but its manufacturing precision demanding, once the leakage is difficult to repair. (4) The main drawback of the ball valve and the plug valve butterfly valve is that the butterfly plate occupies a certain cross-section of the water, increasing the head loss of some; gate valve without this problem, but the height of the large diameter vertical gate valve affects the depth of soil cover, large diameter The length of the horizontal gate valve increases the horizontal area occupied by the pipeline and affects the arrangement of other pipelines. The ball valve and the stopcock maintain the cross section of the gate valve and overcome its disadvantages. Ball valve has the advantages of simple structure, small flow resistance, reliable sealing, flexible operation, easy maintenance and operation. Plug valve also has similar advantages, only the water area is not positive Park. Ball valves and plug valves are heavier than the butterfly valve, casting and processing difficult, the price is more expensive, generally applicable to small and medium-sized pipe. The past ten years due to the improvement of casting technology, the use of lost foam molding or resin sand casting, to avoid or reduce the machining, thereby reducing the cost, so the feasibility of ball valve for large-diameter pipe worth exploring. In recent years, a factory in Hubei Province modeled on the United States products, developed a fan-shaped eccentric plug valve, fan-shaped valve plate lined with rubber, good sealing, opening and closing torque is small, large flow area, and passed the mechanical valve testing center made the valve hoist Durability test and flow resistance test, thus filling the gaps in this type of valve. The current fan eccentric plug valve at the bottom of a groove, easy to slag, easily lead to open and close failure, should be improved. 2.2 The material of the valve (1) the valve in the water supply pipe network, the past valve body, valve cover, gearbox material is gray cast iron, partly ductile iron. In view of pipe, pipe fittings are promoting the use of ductile iron, the valve material should be so. To improve the quality of castings, and reduce the weight of the valve, especially the valve plate should first use ductile iron pieces (QT405-10).