Discussion on the selection of root valves for instruments
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(1) Function: Isolate equipment, pipelines, and instruments to facilitate the removal of instruments and offline maintenance； When selecting, it should not react with the medium, have flexible operation, be easy to seal, not prone to clogging, and require minimal maintenance. (II) Basis: Medium temperature, pressure, viscosity, diameter, and location (primary valve, secondary valve, drain valve). (III) Types: Globe valve, gate valve, ball valve, jacketed ball valve, needle valve. 1. For media that tend to condense or form scale, flanged ball valves and jacketed ball valves are suitable. 2. For 1/2'' and 3/4'' instrument air primary valves, stainless steel three-piece ball valves are generally used ； 3. For analyzing instrument sample gas sampling systems and preprocessing systems, needle valves are generally used ； 4. Gate valves are generally used for the primary steam and water valves ； 5. Globe valves are generally chosen for heavy oil ； (IV) Size: 1/2'' 3/4'' DN50 DN80 (V) Connection methods: welding, threading, flange, sleeve; 1. For low pressure: threading connection ； Those under higher pressure are connected using flanges or welding, while high-pressure applications employ socket welding. (VI) Others 1. Choose dual valves 1) High-temperature and high-pressure media. 2) Toxic and harmful media. 3) One valve for processes, equipment, and pipelines at greater distances, and the second valve for instrument pipelines. 2. No root valve required: plug-in pressure and level transmitters. 2023.8.29
This is indeed a good choice
The selection of the root valve for instruments is based on the following factors: 1. Properties of the medium: A material that does not react with the medium should be chosen to prevent contamination or corrosion of the medium. At the same time, the temperature, pressure, and viscosity of the medium must be considered to determine the valve’s temperature and pressure resistance as well as its fluid characteristics. 2. Valve types: Common root valves for instruments include globe valves, gate valves, ball valves, jacketed ball valves, and needle valves, etc. Select the appropriate valve type based on the properties of the medium and the process requirements. 3. Size: The size of the valve is determined based on the pipe diameter and the requirements of the process; common sizes include 1/2'', 3/4'', DN50, and DN80, among others. 4. Connection method: Select the appropriate connection method based on the application scenario of the valve and its connection requirements, such as welding, threading, flanges, or clamping. 5. Other considerations: If the medium is prone to condensation or scaling, a flanged ball valve or a jacketed ball valve can be chosen ； If it is for analyzing the sample gas sampling system or preprocessing system of instruments, needle valves are generally used ； If it is a primary valve for steam or water, a gate valve can be chosen ； If it is heavy oil, a globe valve is generally chosen. Additionally, the use of a dual-valve system should be considered; for example, in cases involving high-temperature and high-pressure media, toxic or hazardous media, or pipelines to process equipment that are located at considerable distances, a dual-valve safety interlock system can be employed, with a second valve being installed on the instrument pipeline. For plug-in pressure and level transmitters, there is no need to install a root valve. In summary, when selecting a root valve for instruments, it is necessary to take into account factors such as the properties of the medium, the type of valve, its size, and the connection method, and make an appropriate choice based on actual requirements and process specifications. .
Root valves, depending on their function, mostly fall under the pipeline category; one can refer to the pipeline index or material table to determine them
However, the instrumentation specialty needs to be involved in the review process to ensure accuracy, thereby avoiding deficiencies, errors, or inappropriate aspects that could lead to delays later on.
Check according to the instrument data sheet, installation diagram, or the requirements for uniform interface dimensions of the instruments
The selection of one-way valves is still quite uncommon.
Pay special attention to the high-pressure sections of the instruments; for example, high-pressure hydrogen is usually equipped with dual-valve systems