Brief introduction to types, characteristics and s

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Introduction to types, characteristics and selection steps of valves

1 Foreword

valves are used in pipelines. Chenquanxun pointed out that the first step of selecting valves for the control device for handling liquids in the system is to understand the functions of various valves and the valves we hope to achieve the tasks and effects we entrusted after installation

2. Classification of valves

(1) valves are classified as follows according to their functions:

a. on off valves: gate valves, plug valves and ball valves

b. throttle valves: ball valve, needle valve, angle valve, disc pendulum quick drop valve, diaphragm valve

c. check valves: swing, lift and two-piece check valves, bottom valves

d. pressure control valves: pressure reducing valve, pressure relief valve and safety valve

e. special valves:

a. sampling valve

b. flow control valve

c. discharge valve

d. other sample valves

(2) classification by material

a. non metallic valves: PVC, plastic (steel), Teflon 1 New catalyst preparation and utilization technology

b. metal valves

a. ferrous metals: iron, steel, stainless steel, alloy steel, etc

b. non metal: aluminum, copper, etc

(3) process method classification

a. cast valves: valves produced by sand mold, shell mold, dewaxing mold, die casting and other molding methods

b. forged valves: valves produced by die forging, free forging or shot (square) material processing

c. welding manufacturing valves: the body and cover are respectively fabricated by combining welding of several parts. For such valves, attention must be paid to the welding procedure specification and its identification (WPS and PQR)

d. injection molding valves: generally used in the manufacture of PVC, plastic and non-metallic valves

3. Characteristics of various valves

(1) gate valves

gate valves are designed and used when the system at a certain part of a pipeline needs to be fully open and fully closed and the fluid flow can only be generated with a small pressure drop. When a certain part of a system needs to be isolated without considering the control of fluid throttling, the gate valve is very ideal and suitable. When throttling is used, the fluid will flow through the valve seat at a high speed, resulting in erosion of the valve, seat and shell (wire drawing phenomenon), or vibration and damage

(2) ball valves, angle valves and needle valves are called because the ball has a spherical column shape. They are mainly designed for tight closing, frequent switching and throttling when the fluid must control the flow. Their most important feature is effective throttling, which minimizes the wire drawing phenomenon and thus reduces the immersion (erosion) of the valve and valve seat, However, as the valve seat is described in detail in the national standard gb/t 9341 ⑵ 000, the test steps run in the streamline. When the fluid flows through this kind of valve seat, the change of flow direction will produce turbulence in the valve and the decrease of force drop. It can only be used when the head loss caused by pressure drop is not required

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