Valve “Textbook”

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In fluid piping systems, valves are control elements whose primary functions are to isolate equipment from the piping system, regulate flow rates, prevent backflow, and regulate and release pressure. Valves can be used to control the flow of various types of fluids, including air, water, steam, various corrosive substances, mud, oils, liquid metals, and radioactive materials. Since it is very important to select the most suitable valves for piping systems, it is equally crucial to understand the characteristics of valves as well as the steps and criteria for choosing them. Classification of valves: Valves can be broadly divided into two categories: 1. Automatic valves, which operate on their own due to the properties of the medium (liquid or gas) itself. Such as check valves, safety valves, control valves, steam traps, pressure reducing valves, etc. 2. Actuated valves are valves whose operating actions are controlled by manual, electric, hydraulic, or pneumatic means. Such as gate valves, globe valves, throttle valves, butterfly valves, ball valves, plug valves, etc.     Based on structural characteristics, and according to the direction in which the closing element moves relative to the valve seat, they can be classified as follows: Gate type: the closing element moves along the center of the valve seat ； Gate type: The closing element moves along the vertical center of the valve seat ； Plug and ball type: The closing element is a plunger or ball that rotates around its own central axis ； Rotary: The closing element rotates around an axis outside the valve seat ； Disk-shaped: The disc of the closing element, which rotates around an axis within the valve seat ； Slide valve type: The closing element slides in a direction perpendicular to the passage.     By purpose, valves can be classified according to their different functions: shut-off valves, which are used to connect or disconnect the fluid in a pipeline, such as globe valves, gate valves, ball valves, butterfly valves, etc. Check valve use: Used to prevent the backflow of fluid, such as check valves. Regulation devices: Used to adjust the pressure and flow rate of the medium, such as control valves and pressure reducing valves. Distribution use: Used to change the flow direction of the medium and distribute it, such as three-way valves, distribution valves, slide valves, etc. Safety valves: Used to release excess fluid when the pressure of the fluid exceeds a specified value, thereby ensuring the safety of the piping system and equipment; examples include safety valves and emergency valves. Other special purposes: such as steam traps, vent valves, drain valves, etc.     According to the driving method, they can be classified as follows: Manual: Driven by human power using handwheels, handles, levers, sprockets, etc. When a relatively large torque needs to be transmitted, reduction devices such as worm gears and gears are installed. Electric: Driven by motors or other electrical devices. Hydraulic: Driven by (water or oil). Pneumatic: Driven by compressed air.     According to the pressure, based on the nominal pressure of the valve, they can be classified as: Vacuum valves: absolute pressure