Thread Content
Valve Installation, Maintenance and Operation Section 1 Installation The quality of valve installation directly affects its use, so careful attention must be paid to it. (1) Direction and position Many valves are directional, such as stop valves, throttle valves, pressure reducing valves, check valves, etc. If installed upside down, the use effect and life will be affected (such as throttle valves), or they will not work at all (such as pressure reducing valves), or even cause danger (such as check valves). General valves have direction marks on the valve body ； If not, it should be correctly identified based on the working principle of the valve. The valve cavity of the stop valve is asymmetrical from left to right, and the fluid must pass through the valve port from bottom to top. In this way, the fluid resistance is small (determined by the shape), and it is labor-saving to open (because the medium pressure is upward). After closing, the medium does not press the packing, which is convenient for maintenance. This is why the stop valve cannot be installed reversely. Other valves also have their own characteristics. The valve installation location must be convenient for operation ； Even if the installation is temporarily difficult, the long-term work of the operator must be considered. It is best to position the valve handwheel flush with the chest (usually 1.2 meters away from the operating floor), so that it is easier to open and close the valve. The handwheel of the floor-standing valve should be facing upwards and not tilted to avoid awkward operation. The valves of the wall-mounted equipment should also leave room for the operator to stand. Avoid operating with your head up, especially with acids, alkalis, toxic media, etc., otherwise it is very unsafe. Do not install the gate valve upside down (that is, with the hand wheel facing downwards), otherwise the medium will remain in the valve cover space for a long time, which will easily corrode the valve stem, and is contraindicated by certain process requirements. It is extremely inconvenient to replace the packing at the same time. Do not install rising stem gate valves underground, otherwise the exposed stem will be corroded by moisture. When installing the lift check valve, ensure that its valve disc is vertical so that it can lift flexibly. When installing the swing check valve, ensure that its pin is level so that it can swing flexibly. The pressure reducing valve should be installed upright on a horizontal pipe and should not be tilted in any direction. (2) Care must be taken during construction and installation, and avoid hitting valves made of brittle materials. Before installation, the valve should be inspected to check the specifications and models and identify whether there is any damage, especially to the valve stem. It is also necessary to turn it a few times to see if it is skewed, because the valve stem is most likely to be bumped during transportation. Also remove debris from the valve. When lifting the valve, do not tie the rope to the handwheel or valve stem to avoid damaging these parts. It should be tied to the flange. The pipeline to which the valve is connected must be cleaned. Compressed air can be used to blow away iron oxide chips, mud, sand, welding slag and other debris. Not only can these debris easily scratch the sealing surface of the valve, but large particles of debris (such as welding slag) can also block small valves and cause them to fail. When installing a screw valve, the sealing packing (linen plus lead oil or polytetrafluoroethylene raw material tape) should be wrapped on the pipe thread and should not get into the valve to avoid accumulation in the valve and affecting the flow of the medium. When installing flange valves, pay attention to tightening the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with a reasonable gap to prevent the valve from generating excessive pressure or even cracking. Pay special attention to brittle materials and valves with low strength. Valves that need to be welded to the pipe should be spot welded first, then the closing member should be fully opened and then welded shut. (3) Protection facilities: Some valves must also have external protection, which is insulation and cold insulation. Sometimes heating steam pipelines are added to the insulation layer. What kind of valve should be kept hot or cold depends on production requirements. In principle, if the temperature of the medium in the valve decreases too much, it will affect the production efficiency or freeze the valve, so heat preservation or even heat tracing is required. ； Whenever the valve is exposed, which is detrimental to production or causes adverse phenomena such as frosting, it needs to be kept cold. Insulation materials include asbestos, slag wool, glass wool, perlite, diatomaceous earth, vermiculite, etc. ； Cold insulation materials include cork, perlite, foam, plastic, etc. Water and steam valves that have not been used for a long time must be drained of accumulated water. (4) Bypass and instrumentation Some valves, in addition to necessary protection facilities, must also have bypasses and instruments. A bypass is installed to facilitate trap maintenance. Other valves are also equipped with bypasses. Whether to install a bypass depends on the valve condition, importance and production requirements. (5) Packing replacement of stock valves. Some packings no longer work, and some do not match the medium used, so the packings need to be replaced. The valve manufacturer cannot consider the thousands of different media used in the unit. The stuffing box is always filled with ordinary packing, but when used, the packing must be adapted to the medium. When replacing the packing, press it in circle by circle. The seam of each circle is preferably 45 degrees, and the seams between circles are staggered by 180 degrees. The packing height should consider the room for continued compression of the gland. At present, the lower part of the gland must press the packing chamber to an appropriate depth. This depth can generally be 10-20% of the total depth of the packing chamber. For valves with high requirements, the seam angle is 30 degrees. The seams between the circles are staggered by 120 degrees. In addition to the above-mentioned fillers, rubber O-rings (natural rubber resistant to weak alkali below 60 degrees Celsius, nitrile rubber resistant to oil products below 80 degrees Celsius, fluorine rubber resistant to various corrosive media below 150 degrees Celsius), three-piece stacked polytetrafluoroethylene rings (resistant to strong corrosive media below 200 degrees Celsius), nylon bowl rings (resistant to ammonia and alkali below 120 degrees Celsius) and other shaped fillers can be used according to specific circumstances. Wrapping a layer of polytetrafluoroethylene raw material tape outside ordinary asbestos packing can improve the sealing effect and reduce the electrochemical corrosion of the valve stem. When compressing the packing, the valve stem must be rotated at the same time to maintain uniformity around it and prevent it from being too tight. Tighten the gland with even force and not tilt. Section 2 Maintenance Maintenance of valves can be divided into two situations: ； One is custody and maintenance, and the other is use and maintenance. (1) Storage and maintenance The purpose of storage and maintenance is to prevent the valve from being damaged or reducing its quality during storage. In fact, improper storage is one of the important reasons for valve damage. Valves should be kept in an orderly manner. Small valves should be placed on the shelves, and large valves can be arranged neatly on the warehouse floor. They should not be piled randomly, and the flange connection surface should not be allowed to touch the ground. This is not only for aesthetics, but also to protect the valve from damage. Due to improper storage and transportation, the handwheel is broken, the valve stem is crooked, the fixing nut between the handwheel and the valve stem is loose and lost, etc. These unnecessary losses should be avoided. For valves that will not be used in the short term, the asbestos filler should be removed to avoid electrochemical corrosion and damage to the valve stem. Valves that have just been put into storage must be inspected. If rain or dirt has entered during transportation, they must be wiped clean before storage. The inlet and outlet of the valve should be sealed with wax paper or plastic sheet to prevent dirt from entering. The processing surfaces of valves that can rust in the atmosphere should be coated with anti-rust oil to protect them. Valves placed outdoors must be covered with rainproof and dustproof materials such as linoleum or tarpaulin. The warehouse where valves are stored must be kept clean and dry. (2) Use and maintenance The purpose of use and maintenance is to extend the service life of the valve and ensure reliable opening and closing. The thread of the valve stem often rubs against the valve stem nut. A little yellow dry oil, molybdenum disulfide or graphite powder should be applied for lubrication. For valves that are not frequently opened and closed, the handwheel should be turned regularly and lubricant should be added to the valve stem thread to prevent seizure. For outdoor valves, a protective cover should be added to the valve stem to prevent rain, snow, dust, and rust. If the valve is mechanically inactive, lubricating oil must be added to the gearbox on time. Always keep the valve clean. Always check and maintain the integrity of other valve components. If the fixing nut of the handwheel falls off, it must be matched and cannot be used randomly. Otherwise, the upper part of the valve stem will be worn in all directions, gradually losing the reliability of the fit, and even being unable to operate. Do not rely on the valve to support other heavy objects and do not stand on the valve. The valve stem, especially the threaded part, should be wiped frequently, and the lubricant that has been contaminated by dust should be replaced with new one, because the dust contains hard debris, which can easily wear the threads and the valve stem surface, affecting the service life. Section 3 Operation For valves, you must not only be able to install and maintain them, but also be able to operate them. (1) Opening and closing of manual valves Manual valves are the most widely used valves. Its handwheel or handle is designed according to ordinary manpower, taking into account the strength of the sealing surface and the necessary closing force. Therefore, long levers or long wrenches cannot be used to move the board. some people * If you are used to using a wrench, you should be careful not to use too much force, otherwise it will easily damage the sealing surface or break the hand wheel or handle. To open and close the valve, the force should be steady and without impact. Some components of high-pressure valves that impact opening and closing have considered that this impact force cannot be the same as that of ordinary valves. For steam valves, they should be preheated and condensed water should be removed before opening. When opening, they should be opened as slowly as possible to avoid water hammer. When the valve is fully open, the handwheel should be turned slightly to make the threads tight to avoid loosening and damage. For rising stem valves, remember the valve stem positions when fully open and fully closed to avoid hitting the top dead center when fully open. And it is convenient to check whether it is normal when fully closed. If the valve stem falls off, or large debris is embedded between the valve core seals, the valve stem position will change when fully closed. When the pipeline is first used, there is a lot of dirt inside. You can open the valve slightly, use the high-speed flow of the medium to wash away the dirt, then close it gently (do not close quickly or slam it to prevent residual impurities from pinching the sealing surface), open it again, repeat this many times, wash away the dirt, and then put it into normal work. For normally open valves, there may be dirt stuck to the sealing surface. When closing, use the above method to flush it clean, and then officially close it tightly. If the handwheel or handle is damaged or lost, it should be replaced immediately. Do not use a swing wrench to replace it, so as to avoid damage to the four sides of the valve stem, failure to open and close properly, and even an accident in production. Some media will cool down after the valve is closed, causing the valve parts to shrink. The operator should close it again at the appropriate time to leave no slits on the sealing surface. Otherwise, the medium will flow through the slits at high speed and easily erode the sealing surface. During operation, if you find that the operation is too strenuous, you should analyze the reasons. If the packing is too tight, loosen it appropriately. If the valve stem is skewed, notify personnel to repair it. When some valves are in the closed state, the closing parts expand due to heat, making it difficult to open. ； If it must be opened at this time, loosen the valve cover thread by half a turn to one turn to eliminate the stress on the valve stem, and then turn the hand wheel. (2) Precautions 1. High-temperature valves above 200°C are at normal temperature when installed. After normal use, the temperature rises, the bolts expand due to heat, and the gap increases, so they must be tightened again, which is called "heat tightening". The operator must pay attention to this task, otherwise leakage may easily occur. 2. When the weather is cold and the water valve is closed for a long time, the accumulated water behind the valve should be removed. After the steam valve stops steam, the condensed water must also be removed. There is a plug at the bottom of the valve, which can be opened to drain water. 3. Some non-metallic valves are hard and brittle, and some have low strength. When operating, the opening and closing force should not be too large, especially not with force. Also pay attention to avoid collision with objects. 4. When using a new valve, do not press the packing too tightly to ensure that it does not leak, so as to avoid excessive pressure on the valve stem, accelerated wear, and difficulty in opening and closing.