As the core control element in the field of industrial automation, pneumatic valves have become a key solution for accurate control in chemical, food, medicine, water treatment, electricity and other industries with the high efficiency and reliability of compressed air drive. The following is an analysis from the five dimensions of core principle, type classification, control mode, application scenario and selection points: 

 I. Core principle: mechanical conversion driven by compressed air 

 The pneumatic valve converts air pressure energy into mechanical energy through compressed air as a power source, and drives the movement of the valve core to achieve fluid control. Its workflow can be divided into three steps: 

 1. Air source treatment: After the compressed air is generated by the air compressor, it is necessary to remove impurities through the filter, stabilize the pressure of the pressure reducing valve, and lubricate the parts of the oil mist (optional) to ensure the stable operation of the actuator. 

 2. Signal control: The solenoid valve or locator receives electrical signals (such as 4-20mA) or pneumatic signals to accurately control the flow and pressure of compressed air. 

 3. Execution action: Compressed air drives the movement of the piston, film or rack, converts it into the linear displacement or rotation torque of the valve stem, drives the valve core to change the diameter of the channel, and realizes open-off, change of direction or flow adjustment. 

II. Type classification: diversified design to adapt to different working conditions 

 According to the action mode of the actuator, pneumatic valves can be divided into three categories: 

 1. Single-acting pneumatic valve: 

 Principle: Built-in spring reset mechanism, the air source only drives one-way action (such as opening the valve), and the spring is automatically reset (closed or open) when the gas is cut off. 

 Advantages: Fault safety design, suitable for emergency cut-off or scenarios that need to maintain the initial state (such as fire protection system). 

 2. Double-acting pneumatic valve: 

 Principle: Through two five-way solenoid valves to switch the gas path, the gas source alternately drives the two-way movement of the piston to realize the full opening and full closing of the valve. 

 Advantages: fast action, accurate control, suitable for automated systems with frequent opening and closing (such as production line flow regulation). 

 3. Intelligently adjustable pneumatic valve: 

 Principle: Integrated valve positioner, receive 4-20mA analog signal, adjust the gas flow rate through PWM control piezoelectric valve, and realize accurate control of the arbitrary opening of the valve core. 

 Advantages: Closed-loop control, eliminating human errors, suitable for processes that require continuous adjustment (such as chemical reactor feed). 

 III. Control mode: full coverage from simple switch to intelligent adjustment 

 The control flexibility of pneumatic valves is reflected in a variety of control modes: 

 1. Switch control: 

 Principle: The solenoid valve is energized/off to control the opening and closing of the gas path, so that the valve is fully open or fully closed. 

 Application: two-way valve (such as emergency shut-off valve), simple start-stop scenario. 

 2. Adjustable control: 

 Principle: The locator receives the analog signal and adjusts the air flow into the actuator to realize the linear correspondence between the valve core opening and the signal. 

 Application: continuous adjustment of flow, pressure and liquid level (such as cold and hot water flow control in HVAC system). 

 3. The bus protocol control: 

 Principle: Communicate with PLC/DCS system through Profibus, Modbus and other protocols to realize remote parameter setting, status monitoring and fault diagnosis. 

 Application: intelligent factory, Internet of Things system, support multi-device network and centralized management. 

 IV. Application scenario: efficient solutions across industries 

 Pneumatic valves play a key role in many industries with their characteristics of adapting to harsh environments, fast action and accurate control: 

 1. Chemical industry and petroleum: 

 Application: Reactor feed flow regulation, pipeline emergency cut-off, safety interlock system (ESD). 

 Advantages: corrosion-resistant and explosion-proof design to meet the needs of high-temperature and high-pressure medium control. 

 2. Water treatment: 

 Application: Dosage adjustment, filter tank backwash control, pump valve linkage. 

 Advantages: Remote monitoring and automatic adjustment to improve the stability of system operation. 

 3. HVAC system: 

 Application: Central air conditioning cold and hot water flow adjustment to achieve precise control of regional temperature. 

 Advantages: Quickly respond to temperature changes and reduce energy consumption. 

 4. Food and pharmaceuticals: 

 Application: Meet the cleanliness requirements and realize the automatic valve control of the CIP/SIP (online cleaning/sterilization) process. 

 Advantages: Sterile design to prevent cross-contamination. 

 5. Energy and electricity: 

 Application: boiler water supply, cooling circulating water system, dust removal system air gate control. 

 Advantages: Resistant to high temperature and high pressure, ensuring the safe operation of the system. 

 V. Selection points: key parameters to match the working conditions 

 When choosing a pneumatic valve, the following factors should be considered comprehensively: 

 1. Medium characteristics: 

 Type: gas, liquid, steam or corrosive media. 

 Requirements: Choose the valve body material (such as stainless steel, plastic) and sealing form (soft seal, metal seal) according to the medium. 

 2. Valve caliber and pressure level: 

 Caliber: Choose DN15-DN1200 and other specifications according to the flow needs. 

 Pressure: Match the working pressure of the system (such as PN16, PN25). 

 3. Actuator type: 

 Single function vs double function: choose according to the safety needs of the fault. 

 Torque/thrust: calculate the required torque (formula: T=K×Q×ΔP/D², K is the safety factor 1.2-1.5). 

 4. Accessory configuration: 

 Solenoid valve: control the opening and off of the gas circuit. 

 Filter pressure reducer: stabilize the pressure of the air source. 

 Limit switch: feedback the full opening/full closing status of the valve. 

 Locator: achieve precise adjustment. 

 5. Environmental adaptability: 

 Protection level: choose IP68 for humid environment, and choose ExdIIBT4 for explosion-proof areas. 

 Temperature range: Cold-resistant materials should be selected in low-temperature environments.