# How to choose the valve

The selection of suitable valves needs to be checked one by one according to the following procedures, so that the selected valve can meet its function and perform the assigned task.
(1) Valve characteristics and main executive functions To understand the characteristics of various valves and their executive functions, this is the first step in selecting suitable valves. The characteristics, classifications and main executive functions of various valves are the first 2nd and 3rd. This section has been mentioned, and is now summarized into Table 1 and Table 2 for reference.

(2) Caliber or flow (capacity) “shown in Table 3” 　　A. The nominal diameter of the valve may not be the same as the diameter of the flow channel. The selected size is calculated from the condition of the conveying fluid to calculate the required Cv value, and then the Cv Value (refer to the manufacturer’s catalog) to select a suitable valve diameter.　　 B. Cv value is defined as the Cv value of the valve when the pressure drops at 1 when the water at 60 degrees Fahrenheit flows through the valve.　　C.Cv value can calculate the flow rate (Q) flowing through the valve.　　Q=CvΔP=7.9Cv　　P=density of liquid, LB/FT3　　ΔP=pressure drop after passing the valve, PSI

(3) Temperature VS pressure The “temperature VS pressure” of the valve refers to the allowable and safe pressure specified by the valve at a certain temperature (but this pressure is the maximum allowable pressure without impact). 5. Valve structure material The choice of valve structure material is extremely important in the functional life of the valve. However, the general valve structure material is mainly divided into two categories: A. Pressure main material: valve body, valve cover, Bottom cover, bolts, etc. The main factors considered in the selection of pressure main material: 　　a. Fluid temperature and pressure: 　　A) High temperature use: Metal materials generally are in high temperature environments, their tensile strength and life are reduced with the increase of temperature, and their creep The intensity also has an impact.　　B) Low-temperature use: When metal materials are used in low-temperature applications, the toughness of their destruction is drastically reduced, resulting in low-temperature brittleness. b. Corrosion resistance of materials: 　　 valve structure metal corrosion causes: 　　 (A) fluid type (B) concentration (C) temperature corrosion damage form: (A) uniform corrosion (B) pitting corrosion (C) dezincification And peeling.