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Variety of valves, the structure, manufacturing materials, driving methods and connections are different forms. Valves are widely used in every aspect of daily industrial and agricultural production activities and people's daily life. Valve as a fluid line control element, its main role is to isolate equipment and piping systems, and adjust the flow to prevent backflow and adjust the pressure, the most basic function is to change the medium flow direction and flow in the pipeline to ensure that the pipeline The safe operation of the system and the smooth flow of the medium on or off. Valve as a fluid line control element, its main role is to isolate equipment and piping systems, and adjust the flow to prevent backflow and adjust the pressure, the most basic function is to change the medium flow direction and flow in the pipeline to ensure that the pipeline The safe operation of the system and the smooth flow of the medium on or off. First, the main technical performance of the valve 1, the strength and performance The strength of the valve performance refers to the ability of the valve to withstand medium pressure. Valves are mechanical products subject to internal pressure and must therefore have sufficient strength and rigidity to ensure long term use without rupture or deformation. 2, the sealing performance Valve sealing performance refers to the valve sealing parts of the media to prevent the leakage capacity, it is the most important valve performance indicators. There are three sealing parts of the valve: (1) the contact between the two sealing surfaces of the opening and closing parts and the valve seat; (2) the matching place between the packing and the valve stem and the stuffing box; (3) the connection between the valve body and the valve cover . One of the first type of leakage is called internal leakage, which is commonly referred to as lax, it will affect the ability of the valve to cut off the medium. For cut-off valves, internal leakage is not allowed. The latter two types of leakage is called leakage, that is, the medium leaks from the valve to the outside of the valve. Leakage will result in material loss, pollute the environment, serious accidents will result. For flammable, toxic or radioactive media, leakage is even more not allowed, so the valve must have a reliable sealing performance. When we choose the valve, we must emphasize the sealing of the valve. In use, the valve sealing surface should not be subject to any erosion, wear is also extremely small, are not afraid of wear and tear, superior sealing performance can achieve zero leakage inside and outside the seal, save energy, protect the environment and improve work efficiency. 3, the flow of medium flow through the valve will produce pressure loss (both before and after the valve pressure difference), that is, the valve on the flow of media have some resistance to the media to overcome the resistance of the valve will consume some energy. From the energy conservation considerations, to minimize the resistance of the valve on the flow medium. 4, opening and closing force and opening and closing moments Opening and closing force and opening and closing torque is the valve to open or close the force or torque must be imposed. Close the valve, the need to make the opening and closing seat and the seat between the two sealing surface to form a certain seal than the pressure, but also to overcome the valve stem and packing between the stem and nut thread between the stem end of the bearing and Other friction parts of the friction, which must impose a certain closing force and closing torque, the valve opening and closing process, the required opening and closing force and opening and closing torque is changing, the maximum value is in the closure of the final instantaneous or open The initial instant. Valve should strive to reduce its closing force and closing torque. 5, opening and closing speed Opening and closing speed is used to complete the valve to open or close the action required to represent. General opening and closing of the valve speed is not strictly required, but some conditions on the opening and closing speed has special requirements, if any requirements quickly open or close to prevent accidents, and some require slow closure to prevent water hammer and so on, This should be considered when choosing the type of valve. 6, the sensitivity and reliability of the action This refers to the valve for the media parameters change, to make the appropriate response to the sensitivity of the throttle, pressure reducing valve, regulating valve and other parameters used to regulate the medium valve and safety valve, trap, etc. Valve with a specific function, the functional sensitivity and reliability is a very important technical performance indicators. 7, the service life It shows the durability of the valve, the valve is an important performance indicators, and has great economic significance. Usually to ensure the sealing requirements of the opening and closing times that can also be used to represent the time. Second, the direction and position Many valves have a directional, such as the cut-off valve, throttle valve, pressure reducing valve, check valve, etc., if installed flip anti, it will affect the use and life (such as throttle), or simply No effect (such as pressure reducing valve), even dangerous (such as 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. The valve cavity around the valve asymmetry, the fluid to pass through the valve from the bottom up, so that the fluid resistance is small (determined by the shape), open the labor-saving, media pressure does not close after packing, easy maintenance. 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. Third, the construction operation must be careful installation and construction, avoid the impact of brittle materials produced by the valve. 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. Fourth, some of the protection of facilities must also have external valve 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. Five, packing replacement valve, some packing 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.
April 07, 2024