Keywords: Chemical Design; Valve; Selection Method 1 Chemical Design Valve Type 1.1 Gate Valve
This valve is the most commonly used type of valve in chemical plant design. When the gate valve is fully open, the drag coefficient of the fluid is minimized, and the fluid does not change direction when it passes through the valve. Compared with the cut-off valve , gate valve with a relatively small installation size, wide caliber range, the pressure to withstand a wide range of temperature characteristics, chemical design is the preferred type of valve.
1.2 stop valve This valve is often installed in the need to regulate the flow of fluid parts, such as the pump outlet, regulating valve bypass flowmeter upstream. Shut-off valve is mainly closed by the valve seat along the center line to play the role of regulating the size of the flow rate, but its function is not the same as the throttle . Compared with the gate valve, the cut-off valve in the action of friction generated by the smaller, with good wear resistance; sealing valve sealing surface is only one, sealing effect, easy maintenance; cut-off valve opening height is small.
1.3 Check Valves Check Valves, as their name implies, are valves that allow fluid to flow in only one direction and do not allow fluid to flow back to its original path. In the case of fluid downstream, the check valve flap opens automatically; in the case of fluid countercurrent, the check valve flap closes automatically.
1.4 butterfly valve
The structure of the butterfly valve is simple, the size is small, the quality is small and the resistance to the fluid is also relatively small. However, the butterfly valve has flexible opening and closing operations and good use performance in the flow regulation. Under normal circumstances, the butterfly valve is mainly used in pipe diameter, fluid pressure, opening and closing parts of the rapid requirements.
1.5 plug valve
Such valves have good sealing, durability, flexible opening and closing features, and plug the valve cavity is not easy to accumulate fluid, will not cause pollution to other materials, so apply to the high risk of fluid control, or in special Use occasion. However, due to the larger opening and closing torque plug valve, so the cost is higher.
1.6 ball valve
This type of valve is developed on the basis of the plug valve, and the function of the plug valve is similar, but the price is cheaper than the plug valve. In all valve types, the ball valve fluidity, the best sealing, and easy maintenance, fluid resistance, opening and closing operations flexible, with a wider scope of application.
2 chemical design of the valve selection 2.1 The correct choice of the type of valve In chemical design, the correct choice according to the actual situation of the valve type. In actual production, different types of valves will have different effects on chemical production, the characteristics and applicable performance may be different, so the valve must be selected for chemical production needs. Chemical designers to fully understand the chemical production process, as well as the valve installed at the operating conditions, and also have to grasp the performance of various types of valves and the scope of application to predict valve installation and use may encounter problems, on this basis Choose the valve type. Different types of valves its function is different, according to the needs of chemical production links to solve the pressure switch operation problems, the valve selection more targeted.
2.2 The end of the valve to determine the reasonable connection In the valve selection process, to fully grasp the applicability of the valve, it is necessary to choose a suitable valve, but also deal with the valve end of the connection so that the overall installation of the valve to meet chemical production demand. The valve end connection includes welding end, thread, flange connection, of which the latter two are common connections. Threaded connection for the valve diameter of not more than 50mm connection, if more than this standard, it will reduce the sealing of the valve, affecting the overall installation of the valve effect; flange connection for diameter and pressure pipe connections, and the threaded phase Ratio, although its installation and removal of simple, but the flange connection is more cumbersome, high installation costs; in the threaded connection and flange connection are not applicable to the case of welding, although this connection is highly reliable , More able to play the role of sealing, but it is not easy to disassemble, is not conducive to maintenance.
2.3 clear the specific function of the valve chemical designers to clearly understand the basic functions of different types of valves, as well as the valve used in chemical devices can play a role. In chemical design, designers should understand the operation requirements of chemical plant, the properties of the fluid in the pipeline, the characteristics of the fluid medium, the temperature change and the pressure-bearing capacity of the valve. According to the specific operation mode of chemical production, select the appropriate valve, To ensure that the specific function of the valve can be fully exploited. At the same time, also need to take into account the economic cost of valve installation, it is necessary to ensure that the selected valve type of function, but also to ensure that the cost is reasonable.
2.4 The preferred valve material In the valve type of choice, to strictly control the material of the valve, which is to ensure that the valve life and use of the important premise. In the choice of valve housing, internal components, sealing surface material, to understand the valve's working environment, including the media pressure, temperature, physical properties, chemical properties, flow requirements. Especially for the corrosive medium, the valve material must be selected according to the relevant regulations to prevent corrosion, so as to ensure the cleanliness of the medium itself. Do not dwell on the solid particles of the valve material corroded by the medium. Common valve materials, including ductile iron, low alloy steel, malleable iron, gray cast iron, austenitic stainless steel, ceramics and other materials, the choice of valve material, it is necessary to take into account the economy of the valve, but also take into account the service life of the valve and use Performance, to ensure that the valve during the various functions of normal.
3 Conclusion In summary, the chemical design, the valve selection is a more important task, due to the type of valve more, if the wrong type selection, it will have a certain impact on chemical production. Therefore, we must correctly select the valve, the only way to maximize the role of the valve to ensure chemical production safety and stability, which is of great practical significance to enhance the economic efficiency of chemical companies.
 Song Shiwei.Chemical design of the commonly used valve selection strategy analysis [J]. Chemical Industry Management, 2015 (3): 102-103.
 Song Jiongliang, Ren Huan, Zhang Desheng.Characteristics and uses of commonly used chemical engineering valves [J] .Chinese Market, 2015 (8): 84-85.
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