When selecting instruments for design, how should instrument flanges be chosen?

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In automatic control system engineering, sensing instruments and actuating devices are always installed on process pipelines, connected in series within those pipelines, or mounted on equipment. Most of them, such as control valves, flow meters, and level gauges, use flange connections. 1. How to choose the type of flange sealing surface for instruments: The type of flange sealing surface depends primarily on the properties and pressure of the medium being measured. When selecting an instrument flange for design purposes, it is necessary to comply with relevant national and industry standards, such as GB (**), HG (for the chemical industry), JB (for machinery), etc. Under normal circumstances: when the medium pressure is not greater than 1.6 MPa, as originally published on the WeChat official account “Automation Classroom”, a flat flange can be used ； When the medium pressure is not greater than 2.5 MPa, a raised-face flange can be selected ； For media that are high-temperature, high-pressure, flammable, explosive, or toxic, when the medium pressure is not greater than 6.4 MPa, male-and-female flanges should be used ； For mortise-and-tenon face flanges, although they offer excellent sealing performance, they are generally not used except in cases involving highly toxic media or when the medium pressure is not greater than 42 MPa, due to the difficulties associated with their manufacturing and disassembly for maintenance. 2. How to select the pressure rating of the instrument flange: The selection principle is that the pressure rating of the instrument flange should be equal to or higher than that of the pipeline or equipment it is connected to. 3. How to select the standard for instrument flanges: The standard for the instrument flanges chosen should, as much as possible, be consistent with the flange standard of the pipes or equipment to which they are connected.