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What are the steps and basis for the selection of imported valves?

(1) Selection steps

1. Defining the purpose of the valve in the equipment or device, determining the working conditions of the valve: applicable medium, working pressure, working temperature, etc.
2. Determine the nominal diameter and connection method of the pipe connected to the valve: flange, thread, welding, etc.
3. Determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage.
4. Determine the material of the casing and internal parts of the selected valve according to the medium, working pressure and working temperature delivered by the pipeline: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.
5. Select 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, etc.
7. Determine the parameters of the valve: For the automatic valve, determine the allowable flow resistance, discharge capacity, back pressure, etc. according to different needs, and then determine the nominal diameter of the pipe and the diameter of the seat hole.
8. Determine the geometric parameters of the selected valve: the length of the structure, the form and size of the flange connection, the dimension of the height direction of the valve after opening and closing, the size and number of bolt holes to be connected, and the dimensions of the entire valve.
9. Use the existing information: valve catalogue, valve product samples, etc. to select the appropriate valve products.

(II) Basis for selecting the valve While understanding the steps of selecting the valve, you should further understand the basis for selecting the valve.

1. The purpose of the selected valve, the working conditions and the control method.
2, the nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive medium, the viscosity of the medium and so on.
3, the requirements of the valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing level and so on.
4, installation size and dimensions requirements: nominal diameter, connection with the pipe and connection size, size or weight restrictions.
5. Additional requirements for the reliability, service life and explosion-proof performance of the valve. (When selecting parameters, note that if the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop at shutdown, maximum and minimum inlet of the valve Pressure.) According to the above criteria and steps for selecting the valve, the internal structure of each type of valve must be carefully understood when selecting the valve reasonably and correctly, so that the correct choice can be made for the preferred valve. The final control of the pipe is the valve. The valve opening and closing member controls the flow pattern of the medium in the pipe. The shape of the valve flow path allows the valve to have a certain flow characteristic, which must be taken into consideration when selecting the most suitable valve for the pipe system.

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