February 13, 2025
Abstract: As an important industrial automation control equipment, pneumatic control valve is widely used in many fields such as chemical industry, petroleum, electric power, metallurgy and so on. It uses compressed air as the power source, combined with electrical valve positioner and actuator, to realize the precise control of process parameters such as medium flow and pressure in pipeline. In this paper, we will introduce the structural composition, working principle, application characteristics of pneumatic control valve and its importance in industrial production.
I. Introduction
With the rapid development of modern industry, automation control systems are more and more widely used in various fields. As a key control device, pneumatic control valve occupies an important position in industrial automation due to its advantages of simple control, fast response and intrinsic safety. In this paper, we will discuss the structure, working principle and application characteristics of the pneumatic control valve to help readers fully understand this important equipment.
II. the structure and composition of pneumatic control valve
Pneumatic control valve is mainly composed of the following parts:
1. pneumatic actuator: this is the core component of the pneumatic control valve, is responsible for receiving signals from the control system (such as PLC), and will be converted to mechanical action. Pneumatic actuator usually includes pneumatic diaphragm, spring, actuator and valve stem components.
2. regulating valve body: including the valve spool, valve seat and the valve body itself. Spool and seat are the key components to realize the throttling effect, they control the flow and pressure of the medium through the relative position change.
3. valve positioner: used to improve the precision of valve control. Positioner according to the valve stem displacement feedback signal to ensure the accuracy and stability of the valve action.
4. accessories: such as filtering pressure reducing valves, solenoid valves, manual operating devices, etc., used to assist the normal operation of the system.
III. the working principle of pneumatic adjustment valve
The working process of pneumatic control valve can be divided into the following steps:
Signal reception and conversion: pneumatic control valve through the control system (such as PLC) to receive current signals or analog signals, these signals are converted to pneumatic signals through the electrical valve positioner or converter. For example, a common 4-20mA current signal can be converted to a 0.02-0.1MPa pneumatic signal through the valve positioner. This conversion allows the pneumatic actuator to make corresponding actions according to changes in the input signal.
2. Actuator action
When the pneumatic signal enters the pneumatic thin-film actuator, the compressed air pushes the membrane to expand, which in turn pushes the actuator and valve stem, causing the spool to be displaced and changing the opening of the valve. Specifically:
-When the air pressure signal increases, the push rod moves upward, driving the valve stem and spool up, and the valve opens wide;
-When the air pressure signal decreases, the push rod moves downward, driving the valve stem and spool down, the valve closes small.
3. The role of the valve positioner
The valve positioner adjusts the action of the pneumatic actuator in real time according to the displacement feedback signal of the valve stem to ensure that the opening of the valve is consistent with the input signal. When the feedback signal is balanced with the input signal, the valve stops moving, thus ensuring the accuracy and stability of the regulation.
4. Adjustment of medium flow and pressure
The pressure before the valve (P1) is changed to the pressure after the valve (P2) through the throttling effect of the valve spool and valve seat. The specific adjustment process is as follows:
-Pressure regulation: P2 is input into the upper membrane chamber through the pipeline and acts on the top disk, the resulting force is balanced with the reaction force of the spring, which determines the relative position of the spool and seat, thus controlling the pressure after the valve. When P2 increases, the force on the top disk increases, overcomes the spring force, closes the spool, reduces the flow area, increases the flow resistance, and P2 decreases until it reaches the set value.
-Flow regulation: By changing the relative position of the spool and seat, the flow area of the medium is regulated, thus controlling the flow. When it is necessary to increase the flow, the valve is opened; when it is necessary to reduce the flow, the valve is closed.
5. Feedback and regulation
In the whole adjustment process, the valve opening changes, the feedback lever will give the positioner a real-time feedback signal. The positioner adjusts according to this feedback signal to ensure the accuracy and stability of the valve action. When the feedback signal is balanced with the input signal, the valve stops moving and maintains the current opening.
IV. the application characteristics of pneumatic control valve
Pneumatic control valve has the following significant advantages, making it widely used in industrial automation control systems:
1. simple control: the operation and maintenance of pneumatic control valve is relatively simple, does not require complex electronic circuits, reducing the failure rate and maintenance costs.
2. fast response: due to the fast response speed of compressed air power, pneumatic control valves can be completed in a short period of time from the receipt of instructions to the implementation of the whole process of action, improve the response speed of the system.
3. Intrinsically safe: pneumatic control valves do not rely on electric power drive, to avoid the risk of electrical sparks, especially for flammable and explosive places.
4. Strong adaptability: pneumatic control valve can regulate gas, steam, liquid and other media, suitable for different working conditions.
5. Long service life: the structure of the pneumatic control valve is reasonably designed, the material selection is excellent, with high durability and reliability, and can operate stably for a long time.
6. energy saving and high efficiency: through precise control of media flow and pressure, pneumatic control valve can effectively save energy and improve production efficiency.
Typical Application Scenarios
Pneumatic control valves are widely used in the following industries and occasions:
1. chemical industry: used to regulate the flow and pressure of materials in the chemical reactor, to ensure the stability and safety of the reaction conditions.
2. petroleum industry: used in oil wells, oil refineries and other places to regulate the flow and pressure in the oil and gas transmission pipeline, to ensure the safety and stability of the production process.
3. electric power industry: used in boiler water supply system and steam regulation system of thermal power plant to ensure the stability and efficiency of boiler operation.
4. metallurgical industry: used in blast furnace, converter and other equipment cooling water system, gas regulation system, etc., to ensure the safety and stability of the production process.
5. Pharmaceutical industry: used in the pharmaceutical production process of various materials transportation and regulation, to ensure the accuracy of the production process and health standards.
VI. the future development trend
With the continuous development of industrial automation technology, the pneumatic control valve is also constantly improving and perfecting. In the future, the development trend of pneumatic control valve is mainly reflected in the following aspects:
1. Intelligent: the introduction of intelligent sensors and communication modules to achieve remote monitoring and diagnostic functions to improve the degree of automation and reliability of the system.
2. Integration: integrate the pneumatic control valve with other control equipment to form an integrated control system, simplifying installation and maintenance.
3. energy saving and environmental protection: further optimize the design and manufacturing process of pneumatic control valves, reduce energy consumption, reduce environmental pollution.
4. multifunctional: the development of pneumatic control valves with a variety of functions to meet the complex needs of different working conditions.
VII. Conclusion
As an efficient, reliable and safe industrial automation control equipment, pneumatic control valve has been widely used in many industries. Its unique structural design and technical advantages make it an indispensable part of modern industrial production. In the future, with the continuous innovation and development of technology, the pneumatic control valve will certainly show more potential and development space in more fields, providing more perfect solutions for the production and environmental protection of various industries.
