Pneumatic control valve is one of the industrial process control instruments widely used in petroleum, chemical, power, metallurgical and other industrial enterprises. According to the working principle of pneumatic control valves, compressed air is used as the power source, cylinders are used as the actuator, and accessories such as electrical valve positioners, converters, solenoid valves, and positioning valves are used to drive the valves, achieving on/off or proportional adjustment, receiving control signals from industrial automatic control systems, and completing the adjustment of various process parameters such as flow rate, pressure, and temperature of pipeline media. The characteristics of pneumatic control valves are simple control, fast response, intrinsic safety, and no need for explosion-proof measures.
What are the characteristics and uses of pneumatic control valves?
1. Purpose and characteristics of pneumatic control valve: It is a right angle reverse layout that can be used in conjunction with valve positioners to achieve share adjustment; V-shaped valve core is most suitable for various regulating occasions, with a high rated flow coefficient, large adjustable ratio, good sealing performance, active regulating function, small volume, and can be installed vertically. Suitable for controlling media such as gases, vapors, liquids, etc.
2. Characteristics of pneumatic control valve: It is a right angle reverse layout, consisting of accessories such as V-shaped valve body, pneumatic actuator, locator, etc; Having inherent flow characteristics similar to equal percentage; Choose a dual bearing layout, with low starting torque, excellent activity and induction speed; Superb cutting ability.
3. The pneumatic piston actuator uses compressed air as its power source, and through the movement of the piston, the arm rotates 90 degrees in reverse to actively open and close the valve. Its components are: adjusting bolts, actuator box, crank arm, cylinder, cylinder shaft, piston, connecting rod, and universal joint.
4. Working principle of pneumatic control valve: Pneumatic control valve consists of an actuator and a regulating mechanism. The actuator is the thrust component of the regulating valve, which generates corresponding thrust based on the control signal pressure to propel the action of the regulating mechanism. The valve body is a component of a pneumatic control valve that directly contacts the regulating medium and regulates the flow rate of the fluid.
Pneumatic membrane angle regulating valve.
2、 Manual for Pneumatic Control Valve - Operation, Inspection, and Maintenance Instructions for Pneumatic Control Valve:
Although there have been some introductions to air conditioning valves, they are not enough to comprehensively summarize this type of product. For us, especially learners, we still need to constantly learn and understand the relevant knowledge of this type of product, and cannot slack off. Therefore, we will inherit the introduction below, so that everyone may be able to learn more about the relevant knowledge of air conditioning valves.
One is operation.
(1) Pneumatic control valves should undergo system calibration before use.
(2) During the operation of the pneumatic control valve, all bypass valves should be closed, and the control valve should be within the normal working range. It is strictly prohibited to adjust the position of the entire valve stem and compression spring. If there is, immediate punishment should be imposed.
2. Normal inspection.
(1) It is important to check the air source pressure, fasteners, and instruments of the pneumatic control valve for looseness and leakage. If any, it should be processed in real-time.
(2) All connecting components should be checked for tightness, friction, scratches, and deformation.
(3) How is the protection environment of the instrument route, and is the sealing environment at the sealing point excellent.
(4) Is the valve stem running smoothly and is there any sign of corrosion on the valve.
3、 Rain proof inspection.
Firstly, check if the instrument wiring port is damp and there may be signs of water ingress.
4、 Maintenance and upkeep.
(1) Clean and lubricate all components to extend the service life of the pneumatic control valve.
(2) Pneumatic control valves should be regularly removed and lubricated, and the oil storage in the injector should be sufficient. If the amount is insufficient, it should be replenished in real time.
3、 Briefly describe the solutions to noise and cavitation problems in the application of pneumatic control valves:
In application, the noise of pneumatic control valves is the main source of pollution in petrochemical production. Cavitation and noise are two main problems in controlling control valves in high pressure differential fluid. So, what are the reasons for these two issues? How should we solve it? Let's take a look at the editor of the pneumatic control valve manufacturer to clarify one by one.
1. Mechanical vibration - For example, when the spool of a pneumatic control valve moves horizontally in the sleeve, the gap between the spool and the sleeve can be minimized or a hard surface sleeve can be used.
2. Mechanical flowability of media - When media flows in pipelines or pneumatic control valves, noise is also generated. In this case, we will not provide specific explanations, but of course, cavitation can also generate noise.
3. Natural frequency vibration - For example, the valve body and other components of pneumatic control valves have natural vibration frequencies, so the characteristics of the valve body can be changed through special casting and forging processes, and other types of valve bodies can be replaced if necessary.
When the cause factor is the instability of the valve core - if the noise caused by fluid pressure fluctuations due to valve core vibration displacement is usually caused by damping factors such as adjusting circuit actuators, the damping coefficient can be readjusted or vibration reduction facilities can be added in the direction of valve core displacement.
What issues should be noted when selecting pneumatic control valves?
There is not much difference between pneumatic control valves and electric control valves, but the actuator is different. The former requires compressed air source, while the latter only requires power supply, which is more convenient. Pneumatic control valves require equipment such as compressors, which have the advantages of explosion-proof function, simple maintenance, and low failure rate. Therefore, in industries such as chemical and petrochemical, its application scope is far greater than that of electric control valves.
According to different structural forms, pneumatic control valves can be divided into several categories, including pneumatic single seat control valves, pneumatic sleeve control valves, pneumatic double seat control valves, pneumatic three-way control valves, pneumatic cage control valves, pneumatic angle control valves, pneumatic V-shaped control ball valves, pneumatic butterfly valves, etc. The main types of configured actuators include diaphragm actuators, piston actuators, etc. Among them, the control accuracy of diaphragm actuators is slightly higher than that of piston actuators. According to the different types of distribution valve positioners, they can be divided into mechanical and intelligent types, with intelligent ones having higher control accuracy than mechanical ones.
According to the different media, there are also different choices for valve body materials. Commonly used carbon steel, corrosive stainless steel, 304 or 316, 316L and other materials can also choose fluorine lined regulating valves. There are also several special pneumatic control valves: low-temperature control valve, high-temperature control valve, high-pressure control valve, small flow control valve, etc. A single regulating valve is used for working conditions with relatively small pressure differentials. Once the pressure difference is relatively large, a sleeve regulating valve or a double seat regulating valve can be selected. Because the leakage of a double seat regulating valve is relatively large and small, it is not suitable to choose a double seat regulating valve.
A three-way regulating valve is used to combine two fluids into one or two fluids. For situations where the pressure difference is particularly large and prone to cavitation or flash evaporation, multi-stage cage type regulating valves can be selected to gradually reduce the pressure of high-pressure fluids and achieve stable control. Pneumatic V-shaped regulating ball valve is suitable for media containing particulate debris, such as pulp. Due to the shearing of the internal components of the valve, its flow characteristics are close to an equal percentage, and its adjustable ratio is much larger than that of ordinary single seat and sleeve regulating valves, so its application range is becoming increasingly wide. Electric regulating butterfly valves are more suitable for large-diameter applications and offer higher cost-effectiveness.
In summary, users should choose pneumatic control valves correctly according to their actual needs to achieve good performance.