Usage characteristics: The main performance and scope of use of the valve have been determined. The types of valves that belong to the usage characteristics include: closed circuit valves, regulating valves, safety valves, etc; Product types (such as gate valves, globe valves, butterfly valves, ball valves, etc.); The material of the main components of the valve (valve body, valve cover, valve stem, valve disc, sealing surface); Valve transmission mode, etc.

Structural characteristics: It determines some structural characteristics of the installation, maintenance, and other methods of the valve, including the structural length and overall height of the valve, the connection form with the pipeline (flange connection, threaded connection, clamp connection, external thread connection, welded end connection, etc.); The form of sealing surface (insert ring, threaded ring, overlay welding, spray welding, valve body); The structural form of the valve stem (rotating rod, lifting rod), etc.

1. Clarify the purpose of the valve in the equipment or device, determine the working conditions, suitable medium, working pressure, working temperature, etc. of the valve.

2. Clearly specify the nominal diameter and connection method of the pipeline connected to the valve: flange, thread, welding, etc.

3. Determine the method of operating the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electro-hydraulic linkage, etc.

4. Determine the materials of the selected valve casing and internal components based on the medium transported by the pipeline, working pressure, and working temperature: cast steel, carbon steel, stainless steel, alloy steel, stainless acid resistant steel, copper alloy, etc.

5. Choose the type of valve: closed circuit valve, regulating valve, safety valve, etc.

6. Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap valve, etc.

7. Determine the parameters of the valve: For automatic valves, determine the allowable flow resistance, discharge capacity, back pressure, etc. according to different needs, and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole.

8. Determine the geometric parameters of the selected valve: structural length, flange connection form and size, height direction dimensions of the valve after opening and closing, bolt hole size and quantity for connection, overall valve dimensions, etc.

How to choose a valve, pay attention to the following points

1. The purpose, operating conditions, and control methods of the selected valve, as well as the valve specifications and categories, should comply with the 

requirements of the pipeline design documents, and the working pressure should be greater than or equal to the working pressure of the pipeline.

2. The properties of the working medium include working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable or explosive, and the viscosity of the medium.

3. Requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing level, etc.

4. Installation size and external dimension requirements: nominal diameter, connection method and size with pipeline, external dimension or weight limit, etc.

5. Additional requirements for the reliability, service life, and explosion-proof performance of valve products and electric devices. (Note when selecting parameters: If the valve is to be used for control purposes, the following additional parameters must be determined: operating method, requirements for large and small flow rates, pressure drop for normal flow, pressure drop when closing, and inlet pressure for large and small valves.)
Based on the above criteria and steps for selecting valves, it is necessary to have a detailed understanding of the internal structure of various types of valves when selecting valves reasonably and correctly, so as to make the right decision on the preferred valve.

The control of pipelines is valves, and the valve opening and closing components control the flow direction of the medium in the pipeline. The shape of the valve flow passage gives the valve certain flow characteristics. When selecting valves suitable for installation in pipeline systems, this must be considered.