Correct choice of the valve, but also the correct installation, maintenance and operation, so as to give full play to their effectiveness. The installation of the first section of the installation of the valve quality, a direct impact on the use, it must be carefully noticed. (A) the direction and location Many valves have a directional, such as the cut-off valve, throttle valve, pressure relief valve, check valve, etc., if installed flip anti-effect will affect the use and life (such as throttle), or It does not work at all (such as a pressure reducing valve) and can even cause danger (such as a check valve). General valve, there are directional signs on the valve body; if not, should be based on the working principle of the valve, the correct identification. Valve valve cavity around the valve is asymmetric, the fluid to pass from the bottom up through the valve port, so the fluid resistance is small (determined by the shape), open the labor-saving (due to media pressure upward) . This is the reason why the stop valve can not be anti-anti. Other valves also have their own characteristics. Valve installation location, must be easy to operate; even if the temporary installation of some difficulties, but also long-term operator for the sake of the operator. The best valve hand wheel and take the chest (generally from the operating floor 1.2 m), so that more open and close the valve. Landing valve hand wheel to be up, do not tilt, so as not to operate awkward. Wall by the machine valve equipment, but also set aside room for operators to stand. To avoid the sky operation, especially acid, toxic media, etc., otherwise it is not safe. Do not flip the valve (that is, the handwheel down), otherwise it will leave the media long in the bonnet space, easy to corrode the valve stem, but also for some of the requirements of taboo. At the same time changing the packing is very inconvenient. Ming pole valve, do not install in the ground, or corrosion due to moisture exposed stem. Lift check valve, the installation of the valve to ensure that vertical, in order to lift flexible. Swing check valve, the installation of the pin to ensure that the level, so spin Kai flexible. Relief valve to be installed upright in the horizontal pipe, do not tilt in all directions. (B) construction operations must be careful installation and construction, should not hit the valve made of brittle materials. Before installation, the valve should be a check, check the specification model, identification of damage, especially for the stem. Also a few turns to see if it is skewed, because the transport process, the most likely to crash crooked stem. Also remove the debris inside the valve. When lifting the valve, the rope should not be tied to the handwheel or the valve stem, so as to avoid damaging the parts and should be fastened to the flange. The valve connected to the pipeline, be sure to clean. Available compressed air blown iron oxide dust, mud, welding slag and other debris. These debris, not only easy to seal the sealing surface of the valve, including large particles of debris (such as welding slag), but also blocked small valves, so that failure. Install the screw valve should be sealed packing (Ma Ma plus lead or Teflon raw material tape), wrapped in the pipe thread, do not get the valve, so as to prevent the accumulation of the valve, affecting the flow of media. When installing the flange valve, pay attention to symmetrically and evenly tighten the bolt. Valve flange and pipe flange must be parallel, the gap is reasonable, so as to avoid excessive pressure on the valve, and even cracking. Pay special attention to brittle materials and valves with low strength. To be welded with the pipe valve, the first spot welding, and then close the full-open, and then welded to death. (C) protection of some of the valve must have external protection, which is insulation and cold. Insulation sometimes add heating steam line. What kind of valve should be insulated or cold, according to production requirements. In principle, where the valve medium to reduce the temperature is too much, will affect the production efficiency or frozen valve, you need insulation, or even with heat; where the valve exposed, adverse or cause frosting and other undesirable phenomena, you need to keep cold. Insulation materials are asbestos, slag cotton, glass wool, perlite, diatomaceous earth, vermiculite, etc .; cold materials are cork, perlite, foam, plastic and so on. Long-term unused water, steam valve must let go of water. (D) Bypass and instrumentation Some valves, in addition to the necessary protection facilities, but also by-pass and instrumentation. Bypass installed for easy access to the trap. Other valves, also installed by the bypass. Whether to install the bypass, depending on the valve status, importance and production requirements may be. (E) packing replacement valve inventory, and some stuffing is not good, and some do not match with the use of media, which requires replacement of packing. Valve manufacturers can not consider the use of thousands of units of different media, stuffing box is always filled with ordinary packing, but when used, you must make the filler and the media to adapt. In the replacement of packing, to be lap circle into. Seams every 45 degrees is appropriate, laps and lap joints staggered 180 degrees. The height of the packing should consider the room where the gland will continue to be compressed. At this moment, the lower part of the gland should be pressed with appropriate depth of the packing room, which can be 10-20% of the total depth of the packing room. For demanding valves, the joint angle is 30 degrees. Seams between circles staggered by 120 degrees. In addition to the above fillers, but also according to the specific circumstances, the use of rubber O-ring (natural rubber resistant to weak base below 60 degrees Celsius, NBR resistance of oil below 80 degrees Celsius, fluorocarbon rubber resistant to 150 degrees Celsius below a variety of corrosive media) Stacked PTFE ring (resistant to 200 degrees Celsius below the corrosive medium) nylon bowl (resistant to 120 degrees Celsius ammonia, alkali) and other forming filler. Outside the ordinary asbestos packing, a layer of Teflon tape, can improve the sealing effect, reduce the valve stem electrochemical corrosion. When the packing is pressed, the valve stem should be rotated at the same time to keep the circumference uniform and prevent death too much. The gland should be evenly pressed and inclinelessly tightened. The second section of the maintenance of the valve maintenance, can be divided into two situations; one is custody maintenance, and the other is the use of maintenance. (A) Custody Maintenance The purpose of custody maintenance is not to damage the valve in custody, or to reduce the quality. In fact, improper storage is one of the important reasons for valve damage. Valve storage, should be well-organized, small valves on the shelves, large valves can be arranged neatly in the warehouse floor, can not be messy stack, do not let the flange contact surface contact with the ground. This is not only beautiful, mainly to protect the valve will not be damaged. Due to improper storage and handling, broken handwheel, crooked stem, nut looseness of the handwheel and stem, etc., these unnecessary losses should be avoided. Short-term temporary use of the valve should be removed asbestos packing, so as to avoid electrochemical corrosion, damage to the stem. On the just entering the valve, to be checked, such as in the process of entering the rain or dirt, to wipe clean, and then stored. Import and export of valves to use wax paper or plastic sheet sealed to prevent the dirty things. To rust in the air valve surface to be coated with anti-rust oil, to be protected. Place the outdoor valve must be covered with linoleum or tarpaulins like rain, dust-proof items. Store the valve warehouse to be clean and dry. (B) the use of maintenance The use of maintenance purposes, is to extend the life of the valve and ensure the opening and closing reliable. Stem thread, often with the stem nut friction, to be coated with a little yellow dry oil, molybdenum disulfide or graphite powder, play a role in lubrication. Do not often open and close the valve, but also on a regular basis to turn the hand wheel, add thread lubricant on the stem to prevent biting. Outdoor valves, to the stem plus protective sleeve to prevent rain, snow, dust rust. If the valve system to be moving, to be on time to add gearbox lubrication. Always keep the valve clean. Always check and maintain the integrity of the valve parts. If the handwheel fixed nut off, to be equipped, can not make improper use, otherwise the upper part of the stem will be parked square, with the gradual loss of reliability, and can not even start. Import metering pumps do not rely on the valve to support other heavy objects, do not stand on the valve. Stem, especially the threaded part, to be wiped often, to be contaminated with dust to be replaced with new lubricant, because the dust contains hard debris, easy to wear threads and stem surface, affecting the service life. Section III operation For the valve, not only will be installed and maintained, but also will operate. (A) manual valve opening and closing Manual valve is the most widely used valve, its hand wheel or handle, is designed to be an ordinary manpower, taking into account the strength of the sealing surface and the necessary closing force. Therefore, you can not use the long lever or long hand to move plate. Some people are accustomed to using the wrench, should pay strict attention to, do not force too much, otherwise easy to damage the sealing surface, or plate broken hand wheel, handle. Opening and closing the valve, force should be smooth, not impact. Some of the impact of high-pressure valve opening and closing of the various components have been considered this impact and general valve can not wait for Gang. For steam valve, open before, should be preheated, and exclude condensate, open, it should be slow, so as to avoid the phenomenon of water hammer. When the valve is fully open, the hand wheel should be reversed a little, so tight between the threads, so as not to loosen the damage. For the rod valve, remember to fully open and fully closed when the stem position, to avoid the impact of the fully open top dead center. And easy to check when the full closure is normal. If the valve to be off, or plugged between the larger spool seal, valve position will be closed when fully closed. The first pipe, the internal dirt more, the valve can be micro-Kai, the use of high-speed flow of media, it washed away, and then gently shut down (can not quickly closed, fierce closed to prevent residual impurities sealing surface) Open again, so repeated several times, rinse the dirt, then put into normal work. Often open the valve, the sealing surface may be stuck with dirt, shut down also use the above method to flush it clean, and then officially closed. Such as the hand wheel, the handle is damaged or lost, should be immediately fitted, can not be replaced by the board wrench in order to avoid damage to the stem square, opening and closing ineffective, resulting in an accident in production. Some media, after the valve is closed cooling, valve contraction, the operator should be closed again at an appropriate time, so that the sealing surface without fissure, or medium flow through the slit at high speed, it is easy erosion of the sealing surface . Operation, if found to be too strenuous operation, should analyze the reasons. If the packing is too tight, may be appropriate to relax, such as stem skew, should notify the staff to repair. Some valves, in the closed state, the closure of thermal expansion, resulting in open difficult; If you must open at this time, the valve cap can be loosened to a half circle to a circle, eliminating the stem stress, and then the plate hand wheel. (B) Notes 1,200 ℃ high temperature valve, due to the installation at room temperature, and after normal use, the temperature increases, the bolt thermal expansion, the gap increased, it must be tightened again, called "heat tight", the operator To pay attention to this work, otherwise prone to leaks. 2, the weather is cold, long-term closure of water valve, water valve should be excluded. Steam valve stop steam, but also exclude condensate. The bottom of the valve is like a plug of thread, which can be opened for drainage. 3, non-metallic valves, some hard and brittle, and some low intensity, the operation, the opening and closing force can not be too large, in particular, can not make Meng Jin. Also pay attention to the provision of free objects bump. 4, when the new valve is used, the packing should not be pressed too tight, so as not to leak, so that the valve stem is pressed too much, to speed up the wear and tear, and opening and closing effort. Chapter V Inspection, Repair and Life-span of Valve Whether using the new valve or using the repaired valve, the pressure test should be done before installation. The first section, pressure test pressure test, refers to the body strength test. Leakage test, referring to the sealing surface tightness test, these two tests is to check the main performance of the valve. Test medium, usually water at room temperature, kerosene can be used for important valves. Safety valve pressure test, you can use a more stable nitrogen gas, steam or air can also be used instead. For diaphragm valves, use air for the test. (A) Test pressure The test pressure of the valve strength has the following relationship with the nominal pressure: Nominal pressure (Mpa) Strength Test pressure (Mpa) 0.1 0.2 0.25 0.4 0.4 0.6 0.6 0.9 1.0 1.5 1.6 2.4 2.5 3.8 4.0 6.0 6.4 9.6 10.0 15.0 16.0 24.0 20.0 30.0 25.0 38.0 32.0 48.0 It can be seen from the above, the nominal pressure from 0.4Mpa-32Mpa, these commonly used pressure valve, the strength of its test pressure 1.5 times. Valve seal test pressure, equal to the nominal pressure. (B) Test method Pressure test leaks, carried out on the test bench. The structure of the test bench (Figure 5-1), the test bench has a pressing member above, there is a pipeline connected to the pressure test pump. After the valve is compressed, the pressure test pump work, from the test pressure pump pressure gauge, you can read the valve to withstand the pressure figures. When the pressure test valve is filled with water, the air in the valve should be drained. Pressure plate on the top of the test bench, a vent, with a small valve opening and closing. The hallmark of air purging is that all that comes out of the vents is water. After closing the vent, start to boost pressure. Boost process should be slow, not sharp. After reaching the prescribed pressure, keep for 3 minutes, the pressure is unchanged. Figure 5-1 Valve test bench pressure test leak test program can be divided into three steps: 1, open the valve access, water (or kerosene) to fill the valve cavity and pressure to the strength test pressure, check the valve body, bonnet, gasket , Whether the leakage of packing. 2, shut off the valve, pressure on the valve side to the nominal pressure, check whether leakage from the other side. 3, the valve upside down, the opposite side of the test. Section II, the general procedure for maintenance When the valve is removed, the steel word on the valve and the flange connected to the valve, lay the maintenance number, and record the working medium of the valve, working pressure and working temperature for the repair selection Corresponding material. When servicing the valve, it is required to work in a clean environment. First clean the outer surface of the valve or blow with compressed air or with kerosene. But remember to nameplate and other logo. Check the appearance of damage and make a note. Then remove the valve of the other parts, with kerosene cleaning (do not use gasoline to clean, so as not to cause a fire), check the other parts damage, and make a record. Valve body cover strength test. If the Department of high-pressure valves, but also for non-destructive testing, such as ultrasonic testing, x-ray detection. Red ring available on the seal powder inspection, seat, gate (valve) match. Check the valve stem is bent, whether corrosion, thread wear how. Check the degree of stem nut wear. Deal with the problems detected. Body repair welding defects. Surfacing or renewal of seals. Align or replace the valve stem. Repair all other parts should be repaired; can not be repaired replacement. Reassemble the valve. When assembled, gasket, packing to be replaced. Perform strength test and tightness test. Section III, common faults and prevention (A), the general valve 1, stuffing box leakage This is the main run, run, leak, often seen in the factory. Leakage caused by the following reasons: 1, filler and working medium corrosive, temperature, pressure does not adapt; 2, the filling method is wrong, especially the entire root filler into the spin-off, the most prone to leakage; 3 , Stem machining accuracy or surface finish is not enough, or oval, or scored; 4, the valve stem pitting has occurred, or due to lack of protection and open-air rust; 5, stem bending; 6, the filler used for too long Has been aging. 7, the operation is too fierce. 2, Leakage of closed part Leakage of stuffing box is usually called leakage, the leakage of closed part is called internal leakage, the leakage of closed part is in the valve, which is not easy to find. Closure pieces can be divided into two categories; one is the sealing surface leakage (Figure 5-4); the other is the root seal leakage causes of leakage are: 1>, sealing surface grinding is not good; 2> 4>, stem bending and torsion, so that the upper and lower closures are not aligned; 5>, close too fast, the sealing surface contact with the valve stem is not strong; Poor or long-term damage; 6>, improper selection of materials, can not withstand the corrosion of medium; 7>, the globe valve, gate valve for regulating the use of sealing surface can not withstand the impact of high-speed flow medium; After the valve is closed and gradually cooled, so that the sealing surface of the slit, will produce erosion phenomenon; 9>, some seals and valve seat, the valve between the use of threaded connections, prone to oxygen concentration of the battery, corrosion loose ; 10>, due to welding slag, rust, dust and other impurities embedded, or the production system has a mechanical plug off the other parts of the valve, the valve can not be closed. 3, stem lift failure. The reasons are: 1>, operating too much to thread damage; 2>, the lack of lubricant or lubricant failure; 3>, stem bending and torsion; 4>, surface finish is not enough; 5>, with tolerances are not allowed to bite Such as stem and stem nut for the same material, easy to bite; 8>, threaded wave medium corrosion (refer to the dark rod valve or stem in the lower part Of the valve); 9>, the lack of protection of open valves, stem thread sticky dust, or rain and snow rust. 4 other valve cracking: generally caused by freezing. When the weather is cold, the valve should have thermal tracing measures, otherwise the valve should be shut down after the shutdown and the water in the pipeline (if there is a plug at the end of the valve, you can open the plugging drainage). Damage to the handwheel: Crash or long lever caused by violent operation. As long as the operator or other relevant personnel pay attention, can be avoided. Packing gland fracture: Uneven packing force, or gland flaws. Compacted packing, to be symmetrical to rotate the screw, not skewed. Manufacture should not only pay attention to large and key parts, but also pay attention to gland and other minor parts, otherwise affect the use. Valve stem and gate connection failure: Gate valve stem square head and gate T-slot connection in the form of more, sometimes not processed T-slot, so the stem square head wear faster. Mainly from the manufacturing side to solve. But the use of units can also be T-slot for additional work, so she has a certain finish. Double gate valve gate can not compress the sealing surface: double gate tension is generated by the top wedge, some gate valve, wedge material poor (low grade cast iron), the use of wear or break soon. Top wedge is a small piece, replace the original cast iron pieces. (B) automatic valve 1, one of the spring-loaded safety valve failure, sealing surface leakage. The reasons are: ①between the sealing surface debris; ② sealing surface damage. This failure to rely on regular maintenance to prevent. Fault two, the sensitivity is not high. The reasons are: ①spring fatigue; ② spring improper use. Spring fatigue, no doubt should be replaced. Spring misuse, the user does not pay attention to a nominal pressure spring-loaded safety valve, there are several pressure sections, each pressure section has a corresponding spring. Such as the nominal pressure of 16 kg / cm 2 of the safety valve, the use of pressure is 2.5 ~ 4 kg / cm pressure section, the installation of 10 to 16 kg / cm 2 of the spring, although also make do with open, but suddenly high and low Very insensitive. 2, check the valve length See fault: ①valve broken; ② media backwards. Caused by the valve to be broken because: before and after the check valve medium pressure is close to equilibrium and mutual "see-saw" state, the valve do often flap with the seat, some brittle materials (such as cast iron, brass, etc.) made of Valve to be broken. Prevention is the use of valves for the tough material check valve. The reasons for the media back flow are: ①sealing surface damage; ② clip into the impurities. Repair the sealing surface and remove impurities to prevent backflow. The above descriptions of common faults and prevention methods can only serve as a stimulating effect. In actual use, other faults may also be encountered. In order to prevent the occurrence of valve faults actively and flexibly, the most fundamental one is to be familiar with its structure, Material and action principle. Section IV, the valve life Because of the wide range of valve applications, the use of a wide range of media, corrosion conditions vary, so from the national standards to industry standards did not make the life of the valve to make provisions in 1980, the Ministry of Machinery Industry in order to improve Machinery and industrial products and with the quality of the country's high-quality products, developed the "valve industry product quality standards for the" where the gate valve, cut-off first-class products, superior products provided for life requirements; such as Dn ≤ 200 ~ 400 high pressure Valve first-class product number of scratch-resistant 2000 times, superior products for 4,000 times. Due to the particularity of nuclear power plants, all countries have stipulated the service life of nuclear power valves; for example, the United States and France all require 40 years while Japan stipulates 30 years to 40 years. The sixth chapter valve technology development Valve technology, depends on the material science, structural development. In recent years, China's synthetic materials, new alloy steel and new technology development, the use of emerging metal materials, made great progress, these are valve technology to add new content. Such as the development of titanium, due to titanium has a very high affinity for oxygen, can generate a solid oxide protective film, resulting in many strong corrosive medium is passive, showing excellent corrosion resistance, acid, alkali and Widely used in organic matter, stainless steel cuts in some mixed organic acids use only one or two weeks, while titanium valves can be used for long periods of time. In addition, the zirconium metal is another good corrosion-resistant metal. Synthetic materials is an endless stream, such as polypropylene, polycarbonates, nylon and other materials manufacturing valves, has been used in the chemical industry. New ceramic valve is also gradually promote the use of. The new structure is also being introduced, such as the introduction of hard sealing butterfly valve in the country is nearly a dozen things. High temperature and pressure power station valve development, application and so on. New sealing materials; Application of flexible graphite. It is in the graphite lattice immersed in a liquid, and then forcibly vaporized to change the direction of lattice arrangement, thereby changing the brittleness of graphite and become a soft material, he can do gasket and packing, due to the purity of graphite, almost able to withstand all Chemical species, if the nickel wire in the folder to increase the intensity can be used for high temperature and pressure control valves for packing, gaskets. In order to reduce costs and improve competitiveness, all countries in the world have developed large-scale equipment. At present, the largest thermal power generating unit is 1.3 million kilowatts (U.S. and Switzerland) and one 600,000 kilowatt generating unit is capable of generating 200,000 kilowatts of power compared with three 200,000 kilowatt generating units. Equipment unit cost of power down 10 ~ 20%, power station construction costs, unit power, manufacturing hours, steel consumption reduced by 20% A 6 million tons / year refinery and two 300 tons / year oil refinery only a considerable investment 69% of the latter, steel consumption of 53%, covers an area of ​​54%, production costs are 75%, while labor productivity has increased 170% of the largest foreign refinery at present was 36.4 million tons / year, and 20 million More than 20 tons / year. With the development of oil refining pipeline industry has also been rapid development. At present, the longest pipeline has been built 4830 km (Iran). The longest gas pipeline is 7680 kilometers (from Alaska via Canada to the United States) with a maximum diameter of 1420mm and 1620mm. The maximum pipeline pressure 9 ~ 12MPa These lines have strict requirements on the valve, are used remote control. Thermal power also increases with the unit, in order to improve efficiency, its working parameters also increase; standard temperature and pressure subcritical temperature 566 C 16.9MPa starting temperature of 583 ° C 24.6MPa supercritical temperature of 650 ° C ; C 35MPa The above summary, by the large-scale equipment on the valve material, structure, reliability put forward more stringent requirements. More Keywords Search: Valve
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