In the pipeline system, the control valve is the control element, which accounts for about 30% ~ 50% of the pipeline project cost. The main function of the valve is hoist, throttling, regulating flow, isolating equipment and piping, preventing media backflow, regulating and venting pressure, and the like. The valve is also the most complex components of the pipeline, which is generally assembled from multiple components, high technical content. With the rapid development of the petrochemical industry, most of the media in the petrochemical production plant have the characteristics of large toxicity, flammable, explosive and corrosive. The operating conditions are more complicated and harsh, the operating temperature and pressure are higher, the starting period is longer, Once the valve fails, the lighter leads to media leakage, which not only pollutes the environment but also causes economic losses. In severe cases, the equipment stops downtime and even causes a serious accident. Therefore, in the pipeline design, choosing the valve scientifically and rationally can not only reduce the construction cost of the device, but also ensure the safe operation of the production. 1 valve selection points 1.1 Clear valve in the device or device purposes Determine the working conditions of the valve: the nature of the medium, working pressure, temperature and operating control methods; 1.2 The correct choice of the type of valve The correct choice of the valve type is based on the designer's full grasp of the production process, operating conditions as a prerequisite for the choice of valve type, the designer should first grasp the structural characteristics of each valve and performance; 1.3 to determine the end of the valve connection In the threaded connection, flange connection, welding end connections, the first two most commonly used. Threaded valve is the main nominal diameter of 50mm below the valve, if the path size is too large, the connection of the installation and sealing is very difficult. Flanged valves are easy to install and disassemble, but screw-on valves are bulky and expensive, making them suitable for all sizes and pressures of pipe connections. Weld connection for more load conditions, more reliable than the flange connection. However, the welded connection of the valve removal and re-installation are more difficult, so its use is limited to the usually long-term and reliable operation, or the conditions of load moment, the temperature is high occasions; 1.4 valve material selection Select the material of the shell, inner part and sealing surface of the valve, in addition to considering the physical properties (temperature, pressure) and chemical properties (corrosiveness) of the working medium, but also the degree of cleaning of the medium (with or without solid particles) In addition, we must refer to the relevant provisions of the state and the use of the department. Correct choice of the valve material can get the most economical valve life and the best performance. Valve material selection order: cast iron - carbon steel - stainless steel, sealing ring material selection order: rubber - copper - alloy steel-F4; 1.5 other In addition, you should also determine the fluid flow through the valve flow and pressure levels, etc., the use of existing information (such as valve catalog, valve product samples, etc.) to select the appropriate valve. 2 common valve introduction Valve variety, variety of complex, there are gate valve, globe valve, throttle valve, butterfly valve, plug valve, ball valve, electric valve, diaphragm valve, check valve, safety valve, pressure reducing valve, steam trap and emergency shut-off valve , Which commonly used gate valve, globe valve, throttle, plug valve, butterfly valve, ball valve, check valve, diaphragm valve. 2.1 gate valve Gate valve is opening and closing body (valve plate) driven by the valve stem, along the valve seat sealing surface for lifting movements of the valve, you can connect or cut off the fluid channel. Gate valve than the valve sealing performance, fluid resistance, opening and closing effort, with a certain regulatory performance, is one of the most commonly used cut-off valve. The disadvantage is the size, the structure of the valve than the complex, sealing surface easy to wear, not easy to repair, generally not suitable for throttling. Press the gate valve stem thread position is divided into bright rod and dark rod two types. According to the structural characteristics of the gate can be divided into two types of wedge and parallel. 2.2 stop valve Shut-off valve is closed down valve, opening and closing pieces (valve flap) by the stem along the valve seat (sealing surface) axis for lifting movements of the valve. Compared with the gate valve, its regulation performance is good, poor sealing performance, simple structure, easy manufacture and maintenance, fluid resistance larger, cheaper, is a commonly used cut-off valve, generally used for medium and small diameter pipe. 2.3 ball valve Opening and closing of the ball valve is a ball with a circular through-hole, ball with the valve stem to open and close the valve. Simple structure of the valve, the switch quickly, easy to operate, small size, light weight, less parts, fluid resistance, good sealing, easy maintenance. 2.4 throttle Throttle valve in addition to the valve with the cut-off valve is basically the same structure, the valve is throttling components, different shapes have different characteristics, the valve seat of the path should not be too large, because of its opening height is smaller medium flow rate increases Accelerate the erosion of the valve flap. Throttle small size, light weight, adjust the performance, but the adjustment accuracy is not high. 2.5 plug valve Plug valve is a plug with a hole as the opening and closing pieces, plug body with the stem rotation, in order to achieve opening and closing of the valve. Plug valve structure is simple, fast switching, easy operation, fluid resistance, small parts, light weight. Stopcock through-type, three-way and four-way. Straight-through stopcock valves are used to cut off media. Three-way and four-way stopcocks are used to change the direction of the media or to divert the media. 2.6 butterfly valve Butterfly valve butterfly valve body is rotated around the fixed axis 90 ° to complete the opening and closing role. Butterfly valve small size, light weight, simple structure, only a few components. And just turn 90 ° to quickly open and close, easy to operate. When the butterfly valve is fully open, the thickness of the disc is the only resistance to the flow of the medium through the valve body, so the pressure drop across the valve is small and therefore has good flow control characteristics. Butterfly valve flexible seal and metal seal two types of hard seal. Flexible sealing valves, seals can be embedded in the body or attached to the butterfly plate around the sealing performance, both for throttling, but also for medium-sized vacuum pipes and corrosive media. Metal sealed valves are generally more flexible seal valve life, but it is difficult to be completely sealed, usually used for large changes in flow and pressure drop, requiring a good throttle performance of the occasion. Metal seals can be adapted to higher operating temperatures, while flexible seals have temperature-limited defects. 2.7 check valve The check valve is a valve that automatically prevents backflow of fluid. The check valve flap opens under fluid pressure and fluid flows from the inlet side to the outlet side. When the pressure on the inlet side is lower than that on the outlet side, the valve flap closes automatically under the influence of fluid pressure difference and gravity itself to prevent the fluid from flowing backwards. According to the structure of sub-lift check valve and swing check valve. Lifting than the Swing Seal is good, fluid resistance. For the suction inlet of the suction pipe of the pump, the bottom valve should be selected. Its function is to fill the inlet pipe of the pump with water before the pump is flooded. After the pump is stopped, keep the inlet pipe and the pump body full of water to prepare for starting again. The bottom valve is usually installed only on the vertical pipe of the pump inlet, and the medium flows from bottom to top. 2.8 Diaphragm valve Diaphragm valve opening and closing pieces is a rubber diaphragm, sandwiched between the valve body and bonnet. The middle part of the diaphragm is fixed on the valve stem. The valve body is lined with rubber. Because the medium does not enter the valve cover cavity, the valve stem does not need a stuffing box. Diaphragm valve structure is simple, good sealing performance, easy maintenance, fluid resistance. Diaphragm valve is divided into weir, straight-through, right angle and DC. Through the above analysis shows that, under normal circumstances, should be preferred gate valve. It should be noted that in the oil, chemical and other piping systems, valve applications, operating frequency and service ever-changing, to control or eliminate low-level leakage, the most important and most critical equipment is the valve. Reasonable choice of valve can reduce the cost of the device construction, to ensure the safe operation of production. NINGBO JINCHEN CRAFTS GIFTS CO.LT , https://www.jinchenlovecrafts.com
Chemical design commonly used in valve selection guide
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