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Principles of setting and selecting chemical electric valve device

by:Sino Valves     2021-02-25
This regulation applies to the major of chemical process systems. The electric valves mentioned do not include safety valves, steam traps, sampling valves, and pressure reducing valves, but include restrictive orifice plates, blind plates, and other pipe fittings that have similar functions to electric valves. Cut-off valves are used as these valves. The general term for pieces. The function of the shut-off valve is to cut off the fluid or change the flow direction of the fluid. It should be set according to the requirements of production (including normal production, startup and shutdown, and special working conditions), maintenance and safety, and also consider the economic rationality. Electric valve device setting and selection of appropriate category (not model). Valves are an important task for process system professionals when compiling PI diagrams. The content described in this regulation takes into account the general requirements of production and safety. When system majors carry out engineering design with reference to these regulations, they should consider the specific conditions of the project, local meteorological conditions, inter-plant collaboration, device operation requirements, fluid characteristics, user special requirements, and economic efficiency. 1.1.1 Selection of valve types in engineering design Factors to be considered when selecting electric valves are based on the rationality of operation, safety and economy, and the result of comprehensive balance comparison. Before choosing a valve, the following original conditions must be put forward: 1. Physical properties (1) Material status a. The material status of gas materials includes relevant physical data, pure gas or mixture, whether there are liquid droplets or solid particles, and whether there are components that are easy to condense. b. The material status of the liquid material includes: relevant physical property data, whether the pure component or mixture contains volatile components or dissolved gas (it can precipitate to form a two-phase flow when the pressure is reduced), whether it contains suspended solids, and the viscosity of the liquid , Freezing point or pour point, etc. (2) Other properties; including corrosiveness, toxicity, solubility to electric valve structural materials, and whether it is flammable and explosive. These properties sometimes not only affect the material, but also cause special requirements on the structure, or need to improve the pipeline grade. 2. Working conditions under operating conditions (1) According to the temperature and pressure under normal working conditions, it also needs to be combined with the working conditions during shutdown or regeneration. a. The pump outlet valve should consider the maximum closing pressure of the pump, etc. b. When the regeneration temperature of the system is much higher than the normal temperature, but the pressure is reduced, for this type of system, the comprehensive influence of temperature and pressure must be considered. c. The degree of continuity of operation: the frequency of valve opening and closing also affects the requirements for wear resistance. For systems with frequent switching, consideration should be given to whether to install dual valves. (2) Allowable pressure drop of the system a. When the system allows a small pressure drop, or when the allowable pressure drop is not small but does not require flow adjustment, a valve with a small pressure drop, such as a gate valve, a straight-through ball valve, etc., should be used. b. If you need to adjust the flow rate, you should choose a valve type with better adjustment performance and a certain pressure drop (the ratio of the pressure drop to the pressure drop of the entire pipeline is related to the sensitivity of the adjustment). (3) The environment where the valve is located: Outdoors in cold areas, especially for chemical materials, the valve body is generally not made of cast iron, but cast steel (or stainless steel) should be used. 3. Valve function (1) Cut-off: Almost all electric valves have a cut-off function. Gate valves, ball valves, etc. can be used for only cutting off without adjusting the flow rate. For rapid cutting off, plugs, ball valves, butterfly valves, etc. are more suitable. The stop valve can both adjust the flow and cut off. Butterfly valve is also suitable for large flow adjustment. (2) Changing the flow direction: Choose two-way (L-shaped channel) or three-way (channel shaped) ball valve or cock, which can quickly change the material flow direction, and because one valve plays the role of more than two straight-through valves, the operation can be simplified , So that the switching is accurate, and can reduce the space occupied. (3) Regulation: stop valve and plunger valve can meet general flow regulation, needle valve can be used for micro fine adjustment; for stable (pressure, flow) regulation in a larger flow range, throttle valve is better . (4) Check: A check valve can be used to prevent backflow of materials. (5) Electric valves with additional functions can be selected for different production processes, such as valves with jackets, drain ports and bypass valves, and valves with blowing ports to prevent solid particles from settling. 4. Power for opening and closing valves: Most valves operated on-site have handwheels. For those with a certain distance from the operation, sprocket or extension rod can be used. Some large-diameter valves have been designed with motors due to excessive starting torque. Use explosion-proof motors of corresponding levels in explosion-proof areas. Remote control valve: The types of power used include pneumatic, hydraulic, electric, etc., of which electric can be divided into solenoid valves and electric motors. It should be selected according to needs and the energy that can be provided. The characteristics and scope of application of various types of electric valves 1. Gate valve (1) When the fluid flows through the gate valve, the flow direction is not changed. When the gate valve is fully opened, the resistance coefficient is almost the smallest among all valves, and the applicable caliber range and pressure The temperature range is very wide. Compared with the stop valve of the same caliber, its installation size is smaller, so it is the most used type in chemical production equipment. (2) There are two types of gate valve handles: clear rod and dark rod: the open rod gate valve is particularly advantageous when it is used for the alternate switching of two or more sets of the same equipment. The open rod can clearly indicate the switching status of the valve. (3) When the gate valve is half-open, the valve core is prone to vibration, so the gate valve is only suitable for fully open or fully closed situations, not suitable for occasions that require flow adjustment.
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