What Are The Common Faults Of Pneumatic Butterfly Valve Actuators? What Is The Core Cause Of The Malfunction?

Pneumatic butterfly valve actuators has the advantages of simple structure, safety, explosion and stable operation. It is widely used in water treatment, chemical industry, gas and HVAC. Although the failure rate of pneumatic actuators is much lower than that of electric actuators, under the influence of long-term high frequency operation, poor working conditions, improper maintenance and improper selection, there are still some common faults such as abnormal opening and closing, weak movement, seal leakage and inaccurate positioning. Most equipment failures are not caused by natural ageing of components, but by human or environmental factors, such as inadequate working conditions, poor air quality and untimely maintenance. This paper aims to generalize the common high frequency faults of pneumatic butterfly valve actuators, analyze the core causes of various faults, and help operators and maintenance personnel to identify and avoid equipment problems in advance.
The most common faults are weak opening and closing and slow opening and closing. Specific performance of valve opening and closing slowly, insufficient travel, not fully open or close, pipeline media control failure. The core causes of the failure can be divided into two main categories: one is insufficient pressure of gas source, field air supply pressure is below the standard working pressure of equipment, air pressure thrust cannot completely overcome spring resistance and pipe media pressure, resulting in insufficient piston power and slow movement; the other is air path blockage, filter or electromagnetic valve dust accumulation, poor compressed air circulation, insufficient intake volume, which directly leads to actuator power attenuation. In severe cases, intermittent equipment jamming and stop-start failures can also occur.
Cylinder leakage and chamber pressure leakage are typical of pneumatic actuators, which can be divided into external cover leakage and valve stem gap leakage. Leakage faults will directly lead to weak valve opening and closing ability, positioning bias, unable to maintain pressure. The core cause is usually aging, wear or corrosion of the seal. Long-term reciprocation of pneumatic actuators can cause repeated friction between internal sealing rings and gasket, causing wear, hardening and cracking; at the same time, compressed air at industrial sites contains water, oil and impurities that can corrode rubber seals and compromise their integrity. In addition, large differences between long-idle equipment and ambient temperature can also cause seals to age and fail, causing pressure and air leakage in enclosed rooms.
Inadequate valve opening and closing, positioning accuracy deviation, is the main fault affecting pipeline process control. The fault is that butterfly valve plate can not be completely sealed and closed, causing a slight leakage, insufficient opening angle, inadequate flow rate. The core causes of fault can be divided into mechanical fault and debugging fault. The first is gear rack wear, increase transmission clearance, resulting in drive virtual position and rotation angle deviation; the second is loose mechanical screws at both ends, stroke calibration bias, limit position out of control. At the same time, unstable air air pressure fluctuations and local air leaks can lead to inconsistent opening and closing strokes and inaccurate batch positioning.
In safe working conditions, the most dangerous faults are failure to reset the a single acting actuator and failure to return due to gas interruption. Single acting models relies on built-in spring to automatically reset the fault. Once the valve cannot be closed due to gas interruption, it will directly lose the ability of safety protection, causing the control risks of media leakage and process loss. The main cause is spring fatigue, rust, lag or reduced elasticity. Long-term highfrequency compression, wet corrosion and impurity jamming will cause the spring to have uneven distribution of forces and elastic failure, so that it can not bounce and reset properly; meanwhile, piston jamming and residual impurity in the gas chamber will hinder the spring reset action of transmission structure.
The equipment's movement is stuck or blocked, a serious mechanical failure that can cause the valve to completely fail to open and close. Such malfunctions are often caused by environmental impurities and installation errors. Dust, oil, and water vapor from the pipe enters the actuator and settles on the gear rack and piston slide, causing mechanical jamming. In addition, excessive coaxial deflection during installation, twisted stem forces, and external pipeline stress pulling the valve can also cause internal transmission structure misalignment, operation jamming, and forced ventilation and pressure that can easily cause gear, rack breakage and damage.
In general, the failure of pneumatic butterfly valve actuators is mainly caused by five core factors: poor air source quality, aging seal, mechanical wear, inaccurate debugging and corrosion working conditions. Unlike complex faults in electrical equipment, most pneumatic actuator faults can be avoided in advance with basic maintenance such as regular drainage, replacement of seals, calibration of travel and cleaning of air circuits. The failure rate and downtime probabilities of the equipment can be reduced effectively, and the control system of pneumatic butterfly valve control systems can be stable, safe and efficient for a long time.