Discussion on Valve Problem in Water Supply Network of Waterworks

1, the valve in the water supply pipe network in the functional water supply pipe network will send tap water delivered to millions 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, the problem discussion Through the investigation of the use of 20 water company pipe network valve, through the inspection of the ten valve manufacturers, I realized that the valve in the water supply network in the role of a large number, wide distribution, 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 liner valve size 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. This seal has the following problems in use: ① Poor 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: ① rubber 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 It is difficult to grasp; ③ Tianjin and Shanghai plant launched db butterfly valves and flanged butterfly valves, their sealing rubber ring inlaid dovetail groove, there is a certain amount of allowance, you can adjust the pressure when the butterfly valve is closed squeeze ; 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 (qt405-10). It should be noted that, due to the different parts of the body thickness, casting ball is more difficult, there should be appropriate measures to ensure the quality of castings. At present there are still some problems casting body, such as the physical and chemical indicators of ductile iron in addition to individual manufacturers, the majority of lax control, and the use of sand casting, a large number of mechanical processing molding. It is suggested that all manufacturers establish a strict quality control system. For the large number of small and medium caliber valves, the model of lost foam molding is adopted. The large-caliber valves are made of resin sand, and the castings should have effective measures to eliminate the internal stress so as to promote the shot blasting and sand removal measures . Casting defects, welding does not allow the way to eliminate, or should take measures to eliminate the internal stress caused by welding repair, a more rigorous test, and to explain to the user. In the inspection also learned that many valve manufacturers casting the use of outsourcing to solve the way to complement each other, the acquisition of outsourcing parts assembly is also a mode of operation, the key is to control the quality of the outer parts should be strict. Of course, the purchase of low-quality components, a little decoration, buckle their own labels, the sale of high prices should be stopped. (2) Stem recommended 2cr13 stainless steel. (3) stem nut recommended cast aluminum brass or cast aluminum bronze, and the nut hardness and strength greater than the stem. 2.3 The valve opening and closing torque In order to manual or opening and closing of the light machine, the valve opening and closing torque under the working pressure ≤ 240n · m, that is, a person can operate. Hope that the valve manufacturer first optimize the valve structure design, improve the concentricity of the components, moving parts of the contact surface finish, reducing the opening and closing resistance. If only by variable speed gearbox ratio, increase the number of ways to reduce hoist torque is not ideal. To this end, the means of mechanical processing can not be updated, such as a valve factory in Tianjin in order to improve the quality of machining, a large number of computer-controlled machine tools and machining centers, is commendable. 2.4 Stem packing seal Valve drip leakage often appear in the valve stem packing, especially large-diameter valves due to the maintenance of the filler without water, the price is expensive. Therefore, it is very necessary to improve the durability of the sealing packing. On the one hand, the materials are suitable and not easy to be aged. In the other hand, the wear of the packing is very small. In addition, the valve opening and closing times in the pipe network are limited, so it should not be replaced for several decades. In the study of a Shanghai company for all types of valve dn100-2600mm valve shaft packing are used three fine apron and a plastic protective cover, as long as the valve body, valve cover assembly concentricity assurance, apron contact Surface finish is good, according to the company can guarantee ten years of opening and closing without dripping, this valve shaft seal than the herringbone, flexible graphite packing and other simple, and to reduce the opening and closing torque, etc., is worth learning. 2.5 valve gearbox large diameter valve due to the relationship between opening and closing torque, equipped with a variable speed gearbox. The following points are to be observed in the manufacture of such components: (1) The device has an opening and closing limit device on the housing, and the adjusting nut of such device shall be located in the housing. (2) Cabinet structure as small and firm as possible, if the opening and closing operation over, not to crack the box. (3) Transmission structure design is reasonable, when opening and closing can only drive the valve shaft to rotate, do not make it move up and down; transmission parts bite normally, do not produce separation and slipping with load hoist. (4) Gearboxes are often easily soaked in water in areas with a high groundwater level, so the enclosure should be sealed. Some valve manufacturers to the valve shaft packing housing and variable speed gearbox integral whole, once the packing leaks, it is easy to string into the box, which is worth improvement. 2.6 Valve operating mechanism Water supply pipe network usually buried in the pipeline, the valve is well protection, Ming rod valve is not applicable, the valve opening and closing force from the ground operation, so the valve opening and closing should be set side mortise, hand The wheel is not suitable. Opening and closing directions are required to turn the valve clockwise, order should be clear. The opening and closing of the valve should be marked plate, the plate should be observed from the ground, marking the scale of the plate should be cast in the casting, the brush can be phosphor, so eye-catching. Should not use aluminum and other materials, pointer and opening and closing limit scale should be installed before debugging, and locked. Recently, some manufacturers of small and medium-sized gate valve, also designed the appropriate opening and closing logo plate, which is commendable thing. 2.7 Valve Performance and Testing Valves performance and performance evaluation, we should pay attention to the following points: (1) the valve opening and closing in the working pressure flexible, lightweight, under the working pressure with water pressure torque detection torque. (2) close the valve tightly, at 1 1 times the working pressure, no leakage or drip Meet the standard requirements (metal sealed butterfly valve), which requires pressure on both sides of the valve rotation, respectively, testing, and multiple opening and closing Achieve the same effect. Requires a variety of caliber, different types of valves, should be in the manufacturer and testing qualified units, with the life of the load hoist detection. This test also includes the evaluation of the valve shaft sealing effect. (3) stronger ability to over-flow valve. In particular, butterfly valve, butterfly flow resistance to be small, over-current area to be large. This requires a variety of caliber, different types of valves should also be qualified to test units for the determination of flow resistance coefficient. (4) The pressure bearing capacity of the valve body should be consistent with the pipe, that is, the valve is open, the valve can withstand the test pressure requirements of the pipeline. (5) In the study of manufacturers, individual valve plant can dn ≤ 600mm valve life, flow resistance, torque and other tests, many of the valve factory does not have such a means. 2.8 Valve lined with anti-corrosion valve is the product, the appearance of the quality of the product on the one hand the image, on the other hand installed in the valve well, and sometimes soaked in water, and sometimes located in wet space, to prevent corrosion is important. Valve is to transport drinking water equipment, valve lining material must be non-toxic, corrosion-resistant, wear-resistant, to be smooth, so that the flow resistance is small. Especially the butterfly valve butterfly plate, platen, bolts, disc material is very different, prone to electrochemical corrosion, corrosion generated rust extends to the sealing surface, affecting the sealing effect of the valve, so the lining to cover and improve. The ideal approach is the body, bonnet, shot blasting sandbox inside and outside the variable speed transmission, and then for electrostatic spraying non-toxic epoxy resin, you can achieve the above effect. In Tianjin, Shanghai-related companies have a line of small-diameter valves in this area. Most manufacturers inside and outside the body brush anti-rust paint, some paint lead and other harmful substances, does not meet the health requirements. 2.9 Valve manual Valve is a device, the instructions in the equipment factory should indicate the following technical data: Valve Specifications; Model; Working pressure; Manufacturing standards; Body material; Stem material; Sealing material; Packing material; Valve opening and closing direction ; Number of revolutions; Opening and closing of maximum torque under working pressure conditions; Manufacturer's name: Date of manufacture: Weight; Aperture, number of holes, center hole distance of connecting flange, and wish to indicate the length, width and height Control size; indicate the flow resistance coefficient; effective opening and closing times and installation, maintenance precautions and so on. 2.10 Valve procurement National valve manufacturers about more than 2,000, there are more than 100 in Henan Province, some manufacturers only a few people's workshops, so valve manufacturing quality and price sparse large. To this end, it is strongly urged the parties concerned to rectify the valve manufacturing industry, the establishment of quality licensing system, banned counterfeit products. When purchasing the valve, please pay attention to the following points: (1) The purchase of manufacturers not a single, shop around three. (2) The purchase of manufacturers sought ISO9001 quality system certification of the enterprise, and pay attention to the selected product is passed the quality certification of the product. (3) According to the different purposes of the valve, according to the above discussion of the issues mentioned in the argument, mention good technical requirements. (4) higher quality valves, the price is correspondingly more expensive, should be based on the overall situation of enterprises, the performance-cost ratio selected to meet the needs of business products, can not be a model, the same price. (5) valves in the pipe network, opening and closing is not frequent, but to replace the maintenance, but the economic and social benefits of the loss is greater, so buy better quality, long-term maintenance products are not common desire. If for a variety of reasons, the price will be lowered a little, it should focus on product after-sales service timeliness. (6) Valve is equipment, valve packaging should not be overlooked, small-diameter valves should strive for container transport, large-diameter valve to make the appropriate packaging, to ensure the integrity of the valve in the long-distance transport. Flange plate should be added if necessary, to protect the sealing surface of the material does not major changes. (7) Many of the water company to the procurement of the valve should be properly disassembled inspection, re-pressure test, unqualified products, non-payment measures, has a certain effect, there is no product that is currently free inspection. (8) The valve should be stored in the warehouse, if the valve is not large enough to be placed in the warehouse, the open display should also be placed at the bottom of the drainage, should be covered above, and should never be exposed to the sun and rain. Inspection found that many manufacturers have created a new valve on the open air sun and rain, the valve unit is also true, this must be corrected. 2.11 valve assembly (1) the connection of the valve and the pipe In order to facilitate the installation and disassembly of the valve, the valve and the pipe is usually installed on the side to install a reusable retractor, some companies dn ≤ 400mm valve with a single disc coupling Live flange) instead of retaining the retractor. Now some valve manufacturers with retainer retractable valve products, is welcome, but the price is higher than the general price of the valve expansion valve is not reasonable, affecting its promotion. (2) the valve should not be premature to enter the construction site Pipeline construction is a long process, the construction person in charge is often worried about the material supply problems started to attach the valve and other ancillary equipment to the site, or even by installing the station one-time shipped to the scene , So that the valve in the construction site in a few months sun and rain, unmanned, the problem is easy to produce. Proposed pipeline construction process, the way to replace double pipe connection, until the pipe construction is completed, the pipe cleaning debris and valve wells (uphole precast reinforced concrete panels are not covered), and then the valve shipped to the site one by one on the installation Bit, and then completed the finishing work wells. Beijing Water Company large diameter valve installation is to take such measures, it is worth learning. (3) After the valve assembly inspection Inspection and supervision personnel at the valve valve site assembly, the assembly should be checked to see whether the drawings meet the requirements of the operation and management needs; opening and closing inspection, opening and closing instructions read and actual opening and closing situation Is consistent; whether the opening and closing rotation consistent with the specification; large diameter pipe should be drilled into the pipe inspection and cleaning sealing surface; and make acceptance records, the establishment of a good valve technology files. 2.12 valve operation and management Whether the valve can be opened and closed well, not only to select the appropriate valve, product quality, careful construction and installation, but also thoughtful management, can play a "thousand days of military training, the deployment of a temporary" effect. Good operational management is reflected in the following three aspects: technical information is available; valve operation and management well; valve well in good condition. (1) the technical information of the valve Technical information of the valve, including the valve factory instructions; valve after the purchase of qualified single; valve assembly and position card; valve overhaul records. For street changes, the valve card should be updated in time, and strive to establish gis management system. (2) valve operation and management of valve quality management requirements, including the valve should be closed tight or basic tightness; valve shaft seal packing no leakage; valve opening and closing light, indicating intact. Valve operation and management of daily work, including the valve before the opening and closing operation of the single batch of approval records and records of the operation of the improvement; valve regular weekly inspection of the opening and closing records. For long-term did not operate the valve, according to the size of the caliber, set a different week inspection cycle is necessary, generally only open and close the number of activities turn, if you want to make the complete shutdown operation is careful. The discovery of the fault should be put forward corresponding large and medium-sized repair plan, promptly dealt with, in particular, can not be opened after the closure of the valve should be the same as emergency repair burst pipe explosion. (3) Valve well condition Valve well condition including valve well masonry meets design requirements; manhole cover intact and road surface intact; Operates the valve hole accuracy; Well without debris and sewage; No rust on the valve surface. As the valve shaft is a closed space, easy to form anoxic, carbon dioxide levels rise, once the maintenance staff to go down well before the operation without strong blast, ventilation and other measures, it is easy to endanger human life. In conditions permitting, large-diameter valve wells should consider well-well air convection long-term technical measures as well. For valve wells should be regularly touring, timely treatment of buried problems, for the cover is lost, the damage should be treated as emergency pipe burst emergency treatment. Wuhan Water Supply Company proposed pipe network management in the valve as equipment management requirements, the use of gps satellite positioning system, the establishment of valve well coordinate data, the assessment of inspection rules and grading standards, and strengthen management measures worth the same industry reference. This article is based on the original "China Water Science and Technology Committee of the Pipeline Commission Investigation Report," the contents of the appropriate compression and personal opinion to join some of the wrong look at the correction.