Hydraulic pump variable control two

Infrastructure construction is the focus of our country's economic construction. The water supply and drainage projects, especially the large-scale sewage treatment projects, the WTO has entered, the western development has been started, the valve market prospects are excellent. Although the history of our water service has been nearly 120 years and 7 years earlier than Japan, there is still a huge gap and needs to be built. The current situation is that half of the water shortage in our 700-plus cities and 100 cities are seriously water-scarce. The average annual water consumption will increase by 7 million m3 / d. In particular, one of the key environmental pollution control measures proposed in the "Ninth Five-year Plan" period in China is sewage treatment, which focuses on the three lakes (Taihu Lake, Chaohu Lake and Dianchi Lake) and the Three Rivers , Liaohe and Haihe). At the same time, 640 county-level cities above 500,000 should be required to build at least one urban sewage treatment plant by 2003. The sewage treatment rate will be 25% during the Ninth Five-Year Plan period and 46% in 2010, That is 1000 plants. At present, there are sewage treatment plants in more than 200 prefecture-level cities in the country, and sewage treatment plants will be built in nearly 400 cities in the next few years. By 2003, we will invest 180 billion to control urban sewage. From 2000 onwards, we will invest 60 billion yuan each year, and equipment investment will reach 20 billion yuan each year. Valves also occupy a small share. A medium-sized sewage treatment plant will need a valve investment of about 600-800 yuan Million In addition, water supply projects, utilities, chemical industry demand is also great. By 2008, Beijing will invest 1800 billion yuan for hosting the Olympic Games, most of which will be used in capital construction. In infrastructure construction, the number of valves will also be substantial. The above situation is only for the domestic market. After entering the WTO, we can see that the market in China is only a small one. Larger markets are in foreign countries. Now that we have entered the globalization, we must make full use of the advantages of our valve industry and actively move toward the world economy platform. A few topics briefly in the valve design, production status, application and development overview. After the reform and opening up, with the vigorous development of China's economic construction, the valve industry has also shown a thriving vitality. There are thousands of valve factory size, despite the mixed, but the product variety has reached more than 3,000 models, nearly 30,000 specifications. In the sealing performance, strength requirements, regulatory function, performance and flow performance, especially the sealing performance, have made great strides, back 10 years, the authority of urban water supply associations have industry famous saying "ten valves and nine leaks" Although some exaggeration, really unsatisfactory. Example: September 1989 - December Chengdu Water Company into the factory test valve 145, with a pass rate of 72.5% in 1996, 917 test pass rate of 88.66%, due to the means of inspection, can not be accepted according to national standards, such as strictly in accordance with national standards Pass rate is lower, the gate valve is mainly poor sealing performance, butterfly valve operating mechanism and so poor reliability, etc., this situation does have significant improvements, and now ductile baht, resin sand casting process, austenitic stainless steel valve shaft, hard Sealing valve seat, special special valve varieties, the application of anti-corrosion spray coating, as well as sealing structure design and other technologies, material problems many manufacturers have mastered, and some (a few) some of the manufacturers of products close to and reached the international advanced level, to replace the imported products , Or export to foreign countries, the overall level is also constantly improving, and further narrow the distance with foreign advanced level. However, due to the overall level of China's machinery manufacturing industry is not high, so the valve needs to be further improved. 2 Commonly used valves Medium and low pressure valves are widely used in urban, construction and corporate water supply and drainage projects. Especially, low pressure large diameter valves (low pressure valves refer to valves with nominal pressure PN≤1.6MPa) and medium pressure valves (PN2. 5-6.4MPa) less, according to the principle and structure classification (commonly used international methods) commonly used valves are butterfly valve and gate valve, the other or the ball valve, check valve, exhaust valve, plug valve, diaphragm valve, pressure reducing valve, Valve, mud valve and so on. 2.1 The status and development of gate valve Gate valve use the longest history, the world is still in use, especially DN300mm below, still occupy the leading position in all kinds of valves. According to the valve plate shape is divided into parallel gate valve and wedge gate valve, wedge gate valve is more common in the international community, characterized by differential pressure before and after the valve plate so that the valve plate is forced on the outlet side of the valve seat, good sealing, and fully open When the valve plate does not remain in the flow path, the pressure loss is small. Used to cut the medium in the pipe. The disadvantage is the operating torque, easy to operate the valve body, stem damage, especially the large gate valve. Dimensions and weight are also large, DN1000 diameter gate valve about 3200mm high, requires four people to operate, so the valve is generally suitable for small-caliber, that DN500 the following. Valve from the open to the middle of the opening, the valve flow resistance is small, close to fully closed, the sharp increase in flow resistance. In the larger range, the change of flow resistance is smaller. When the flow is close to fully closed, the flow rate changes greatly. Do not use it when the valve is close to close. In this case, it is very difficult to fine-tune the flow rate. If the valve opening is extremely small, the flow velocity at the opening is very fast, cavitation will be generated on the underside of the gate, and accompanied by intense vibration noise, long time throttling operation, often make the valve body and gate metal Cavitation. If the gate valve operating conditions in the middle of the opening, because the valve plate is supported by the rail on both sides, fully closed with close, and the middle position, the valve plate and the guide rail gap and produce vibration. Therefore, even in the area where the cavitation rate is low, the valve is throttled for a long period of time, the guide rail may be deformed, worn or damaged. Since the valve seat is not in full contact but the pressure on the surface of the contact portion is high, Bite or adhesion, therefore, should not be used for flow control. Also note that the gate valve in a small opening, the flow changes, if the valve emergency opening and closing, is caused by a sharp increase in pressure or negative pressure, especially when the valve is closed when the water hammer. Based on the metal seal gate valve, the soft rubber sealed gate valve has been developed in recent years. Its features are: (1) There is no concave at the bottom of the valve body, and the fluid passes the straight line in cross section, which makes it difficult to pile up and trap foreign matters. ? (2) Gate sealing surface is pressed on the valve body to stop water, the valve torque off. ? (3) Not affect the sealing performance due to bending and stretching of piping. (4) The entire valve lining rubber, corrosion-resistant, no rust. (5) The valve can change the sealing material and O-ring at the same time when the water is fully turned on. Due to the superior function, the international (especially in Europe) the rapid increase in demand, soft seal gate valve invented Austrian 30 years ago in Europe each year to produce more than 500,000 units, almost 100% of the use of hard seal valve is an alternative, Its manufacturing caliber in Europe and Japan as DN500, the United States generally used DN400, while Italy can produce to DN1200. 2.2 The status and development of butterfly valves In the 1930s, the United States invented the butterfly valve, which was introduced into Japan in the 1950s and was generally used in Japan until the 1960s. However, promotion in our country was something after the 1970s. At present, butterfly valves of DN300 mm or above have gradually replaced gate valves in the world. Compared with the gate valve butterfly valve has a short opening and closing time for the moment of small, small installation space and light weight. Take DN1000 as an example, the butterfly valve is about 2T, while the gate valve is about 3.5T, and the butterfly valve is easy to combine with various driving devices, and has good durability and reliability. ? The disadvantage of rubber seal butterfly valve is used for throttling, due to improper use will produce cavitation, rubber peel, damage and so on. To this end, the international development of metal seal butterfly valve, cavitation area decreases in recent years, China has also developed a metal seal butterfly valve in Japan in recent years also developed cavitation-resistant, low vibration, low noise comb-shaped butterfly valve. General seal seat life under normal circumstances, rubber 15 years - 20 years, metal 80 years - 90 years. But how to choose correctly according to working conditions. Butterfly valve opening and the relationship between flow, basically a linear change in proportion. If it is used to control the flow, its flow characteristics are closely related to the flow resistance of the pipe. For example, the diameters and forms of the valves installed in the two pipes are all the same, while the pipe loss coefficient is different, and the flow difference of the valve will also be very large. ? If the valve is in a state of large throttling, the back of the valve plate is prone to cavitation, the possibility of damage to the valve, are generally used outside the 15 °. When the butterfly valve is at the opening, the shape of the opening formed by the valve body and the front end of the butterfly plate is centered on the valve shaft, and the two sides form a different state. The front end of the butterfly plate on one side moves in the direction of flowing water while the direction of the counter flow Therefore, one side of the valve body and the valve plate is formed like a nozzle-shaped opening, the other side is similar to the orifice-shaped opening, the nozzle side is faster than the throttling side of the flow rate, and the throttling side valve generates a negative pressure below, Rubber seals tend to come off. Butterfly valve operating torque, due to the opening and the valve opening and closing direction of different values, horizontal butterfly valve, especially large-diameter valve, due to the depth of the valve shaft, the difference between the head and the resulting torque can not be ignored. In addition, the valve inlet side of the device elbow, the formation of bias current, the torque will increase. When the valve is in the middle opening, the operating mechanism needs self-locking due to the water flow moment. Figure shows the flow characteristics of butterfly valve installed in the pipeline, K is the loss factor of the entire pipe except the butterfly valve, K is zero when the valve characteristics of the inherent characteristics that K value is large, such as K is 100, the valve even closed 50%, and the same as the full flow. 2.3 Improvement of the exhaust valve? The old two-port exhaust valve due to small exhaust capacity and other reasons, and gradually be replaced by the new high-speed intake and exhaust valves. This float ball valve was successfully developed by the Municipal Design and Research Institute of Beijing in the early 1980s and passed the appraisal. At the same time, Japan has also successfully developed it in about the same time. And our own developed single orifice, orifice vent valve, respectively, according to a certain way to install the pipe to eliminate the role of pipe water hammer. Exhaust capacity is several times the old exhaust valve. The valve inside the exhaust channel symmetry demanding, so the installation of a higher requirement, the inclination angle of not more than 1.5 degrees. 2.4 The development of multi-function control valve? The valve is the media itself as a power source pressure pipeline, the opening and closing, regulation, the pilot valve and the system of different combinations of small pipes, can have nearly 30 kinds of functions, and now gradually get more common use. ? Pilot valve by the control object as the water level and pressure changes and action, as a large number of pilot valve can be used alone or in combination, you can get the main valve on the water level and pressure and flow, etc., separately or in combination Function But the main valve is similar to the globe valve, the valve is fully open, the pressure loss is much larger than other valves, and each opening loss coefficient is more close with the full closure, the more drastic increase in valve diameter is more significant. Valve with the above characteristics, near full closure, the valve action is accelerated, prone to water hammer (water impact pressure), close to fully closed, the slower the valve action as possible, so you can set the valve flap Flow institutions. In addition, the pilot valve throttling and the action part should try to avoid setting a special small aperture to avoid clogging. If necessary, add filters, regular maintenance and set up by-pass pipeline. This valve development, the use of promising. 3 Two important parameters need to be further deepened? Valve flow coefficient and cavitation coefficient is an important valve parameters, which are generally available in advanced industrial countries, the valve material can be provided, even in the sample also printed. China's production of the valve is basically no information in this area, because access to this information need to do experiments can be made, this is our country and the world's advanced level of the valve one of the important performance gap. 3.1 The flow coefficient of the valve The flow coefficient of the valve is an indicator of the flow capacity of the valve. The larger the value of the flow coefficient, the smaller the pressure loss when the fluid flows through the valve. According to KV value calculation formula: KV-flow coefficient Q-volume flow m3 / h ΔP-valve pressure loss bar P-fluid density kg / m3 ?? 3.2 Cavitation coefficient of the valve? With cavitation Coefficient δ value, to select the control flow, the choice of what type of valve structure. Where: H1 - after the valve (outlet) pressure m? H2 - atmospheric pressure and its temperature corresponding to the difference between the saturated vapor pressure m? ΔP - before and after the valve pressure difference m? Various valves due to different structures, therefore, allowed cavitation The coefficient δ is also different. as the picture shows. If the calculated cavitation coefficient is greater than the allowable cavitation coefficient, then it is available and no cavitation will occur. If the butterfly valve allows a cavitation coefficient of 2.5, then: • If δ> 2.5, cavitation does not occur. When 2.5> δ> 1.5, slight cavitation can occur. When δ <1.5, vibration occurs. δ <0.5 continued to use the case, it will damage the valve and downstream piping. The basic characteristics of the valve and operating characteristics of the valve, the valve cavitation occurs at a time when it is out of sight, not to mention that at that point to reach the operating limit. Through the above calculation is clear at a glance. Therefore, cavitation occurs because the liquid accelerates the flow through a section of the tapered section, the part of the liquid gasification, the resulting bubble followed by the valve after the open section burst, the performance of three :? (1) the occurrence of noise (2) vibration (In severe cases, it can cause the destruction of foundation and related structures, resulting in fatigue fracture.) (3) Material damage (erosion of valve body and pipeline) • From the above calculation, it is easy to see that cavitation and post-pressure H1 There is a great relationship, increased H1 will obviously change the situation, to improve the method:? A. The valve installed in the pipeline lower. b. Install orifice plate on the pipe behind the valve to increase resistance. c. Valve outlet is open, direct reservoir, so that the bubble burst space increases, reduced cavitation. ? Comprehensive analysis of the above four aspects, discussion, summed up the gate valve, butterfly valve main features and parameter list easy to use. 4 valve standards must pay attention to Now the State Council set up a standardized management committee and the Bureau of Standards, standardization has been the country attaches great importance to improve our products is an important means of WTO entry is an important response. At present, China has more than 19,000 national standards, more than 23,000 local standards, corporate standards more than 80,000 items. Among them, 43.5% have adopted international standards, accounting for only 25% of the equivalent of international standards. Valve has a national standard of about 60, more than 180 industry standards, many of the special, there is no special valve national or industry standards, urgent development. In terms of standard-setting, the state has formulated guidelines and policies for reform, starting from the four aspects of management system, system, operation mechanism and working mode. In the future, the formulation of standards should focus on enterprises, be open and transparent, involve them extensively, and enhance their leadership and social values. 5 water supply and drainage engineering valves should pay attention to several issues? 5.1 water supply and drainage projects commonly used valves and other industries, as the general valve, such as butterfly valves, gate valves, check valves, but also with professional features Special valve. Such as the exhaust valve, slow closing check valve, flow control energy dissipation valve, control valve, fire signal valve, stop water hammer elimination valve (water hammer eliminator), anti pollution check valve, silencer valve and so on. And foreign comparison, the more common varieties of valves, but the larger the gap between the special valve needs to be filled. 5.2 The inner wall paint for the water supply engineering valve must be non-toxic, and approved by the health and epidemic prevention supervision department above the provincial level to use. The valves used for sewage projects should be corrosion-resistant and not easily clogged, while the sludge discharge is more quickly opened and closed straight channel structure type, such as soft seal gate valve; the use of butterfly valve fastening bolts austenitic stainless steel, convex and concave part Easy to catch fibers, and should be installed. 5.3 The operating mechanism should be a worm gear drive, and designed to be self-locking, that is, indexing guide angle λ is less than the equivalent friction angle between gear teeth φ, and the flank backlash is smaller or the head sloshing. 5.4 Butterfly valve inlet pipe set up or equipped with a pump can not be too close, because the flow is turbulent when the valve will vibrate. 5.5 Before or after the valve is too close to the elbow, because of uneven force, the tightness of the valve seat. 5.6 pump suction pipe should be installed in the linear butterfly valve, eccentric butterfly valve should be installed when installed as well, or double suction centrifugal pump imbalance in water. 5.7 large-diameter butterfly valve mounted, the torque to 0.2 times larger, configure the valve operating mechanism should pay attention. The media is not suitable for lying on the net, when the shaft loading shaft bearing conditions are good. 5.8 When the butterfly valve is used as a flow control valve, it should not be used within the opening of 15 °. It will cause vibration and cavitation. When the valve is in a small opening, the closing speed must be slow, otherwise it will cause the valve to close the water hammer. 5.9 gate valve and butterfly valve main performance parameters for reference. Valve type Valve butterfly valve Metal seat Rectifier, comb tooth Main applications Cutting control, cutting and cutting, control Permissible flow rate (m / s) 3 (6) 3 (6) 6 6 Seat sealing is good and there are a few Leaky excellent valve seat durability Excellent rubber flaws Disadvantages Excellent Full open loss coefficient of 0.1-0.2 0.3 0.3 0.8 Permissible cavitation system 3.0 2.5-4.0 1.5-3.5 0.9-3.0 Flow control characteristics unsuitable than the cavitation zone than the rubber Seat like the metal seat is good Drive mode Manual, electric, hydraulic Manual, electric, gas hydraulic With the same left Features 1. Use a small aperture suitable 2. The pressure loss at full open 3. The pressure loss is small when closed 4. Body groove Easy to accumulate things and lax 5. Open a long time 6. The operating torque of large 1. Simple structure 2. All closed water impermeability 3. Short opening and closing time 4. Operating torque 5. Small size and light weight 6. Cavitation will cause the rubber peel off 1. Simple structure 2. Good control characteristics 3. Short opening and closing time 4. Small operating torque 5. Small size and light weight 6. Good seat durability 7. A small amount of leakage 1. Good control characteristics 2. Fully closed when the water is good 3. Opening and closing time is short 4. Small operating torque 5. Small size 6. Structure slightly Complex 7. Cavitation resistance is good