How to Maintain Efficient Pneumatic Control Valve Operation

To ensure the long-term stable and precise operation of pneumatic control valves in industrial production, and to avoid failures and downtime caused by improper operation or untimely maintenance, operators must fully understand their working principles and usage precautions. Detailed management and timely intervention during daily operations, inspections, and maintenance can significantly extend the valve's service life and improve the overall efficiency of the system. This article will explore in detail how to ensure the efficient and safe operation of pneumatic control valves under various working conditions through scientific operation methods, preventive maintenance, and timely problem resolution, thereby providing continuous and stable control functions for the production system.

Avoid Prolonged Operation at Small Openings

When pneumatic control valves operate at small openings, they experience severe flow resistance, velocity, and pressure fluctuations, leading to a series of potential issues, including:

Sealing Surface Wear: When the valve core's sealing surface approaches the throttle port, the throttle gap is minimal, and the flow velocity is extremely high. This causes erosion of the sealing surfaces of the valve core and seat, leading to rapid wear and significantly shortening the valve's service life.

Reduced Stability: When the rapid changes in flow velocity and pressure exceed the actuator's stiffness, the valve's operational stability is greatly reduced, potentially causing severe oscillation.

Jump Phenomenon: In a flow-closed state, the valve may exhibit jump closing or jump starting, which can prevent normal regulation and affect the stable operation of the entire system.

Special Valve Issues: For example, butterfly valves may experience significant unbalanced torque at small openings, causing them to jump open or closed. Double-seat valves may become unstable and oscillate due to the different flow states of the two valve cores.

To ensure the valve's service life and regulation accuracy, pneumatic control valves should avoid prolonged operation at small openings. It is recommended to maintain the valve opening between 10% and 15%.

Avoid Frequent Switching of Pneumatic Control Valves

Frequent switching of pneumatic control valves near a certain position can lead to the following issues:

Seal Damage: The actuator's seals and packing seals can wear out due to frequent movement, leading to reduced sealing performance.

Positioner Damage: For control valves with intelligent valve positioners, the potentiometer can fail due to frequent switching, causing the valve to lose its positioning function and precise control.

To avoid these issues, operators should minimize frequent switching near a certain position, especially during prolonged operation, to maintain stable valve operation.

Prevent Long-term Use in Vibrating Environments

Long-term operation of pneumatic control valves in vibrating environments can significantly increase the failure rate and shorten the service life of the valves and related control accessories. Vibration-related issues include:

Component Wear: The valve stem guide components can wear out due to vibration, causing abnormal vibration of the valve stem, leading to damage and deformation of internal components and affecting normal operation.

Accessory Damage: Control accessories such as solenoid valves and positioners can be affected by vibration, significantly shortening their lifespan and potentially causing premature failure.

Therefore, pneumatic control valves should avoid long-term use in vibrating environments, especially in high-frequency vibration scenarios. If use in such environments is necessary, regular inspections and maintenance should be conducted.

Prohibit Operation Under Overpressure and Over-temperature Conditions

Operating pneumatic control valves under overpressure or over-temperature conditions can lead to the following issues:

Seal Damage: Under high temperature and pressure, the internal seals of ball valves may deform or fail, causing internal leakage or sticking.

Structural Damage: Under overpressure and over-temperature conditions, the sealing surface coating of the valve may be damaged, leading to damage of the valve ball or seat and severely affecting the valve's normal operation.

Therefore, pneumatic control valves should strictly avoid operation under overpressure and over-temperature conditions, ensuring that the working environment's pressure and temperature are within the valve's design range.

Key Issues and Handling During Inspections

During on-site inspections, the following phenomena should prompt immediate contact with instrumentation maintenance personnel for inspection and handling:

Air Leakage: If air leakage is detected at any part of the actuator or control accessories, instrumentation personnel should be notified immediately for inspection and repair.

Medium Leakage: If medium leakage is detected at the valve stem packing, it may indicate seal damage and requires immediate attention.

Abnormal Exhaust: Continuous exhaust from the control accessory's exhaust port may indicate a fault in the valve or actuator.

Valve Abnormalities: During operation, if the valve actuator exhibits abnormal phenomena such as panting, sticking, crawling, noise, or oscillation, timely handling is required to prevent minor issues from escalating into major failures that could affect the stable operation of the entire process system.

Timely detection and resolution of these issues can prevent minor faults from developing into larger problems, ensuring the stability of the valve and the entire system.

Operation Methods and Precautions for Handwheel Mechanisms

Pneumatic control valves typically do not require frequent manual operation. However, in emergencies (such as during startup, shutdown, or accident conditions), control valves with handwheel mechanisms can provide manual operation to ensure system safety. Common handwheel mechanisms include:

Side-mounted Handwheel: This handwheel mechanism can be directly operated to drive the valve in one direction.

Adjustable Direction Handwheel: Includes side-mounted and top-mounted structures, allowing the handwheel to drive the valve open or closed.

Switchable Handwheel: This type of handwheel requires turning the switch, pulling out the limit pin, and then switching to manual operation mode before performing open or close operations.

Worm Gear Mechanism Handwheel: This handwheel mechanism requires rotating the handwheel to drive the internal worm gear mechanism, moving the threaded sleeve up and down until the positioning hole aligns with the valve stem positioning hole, then inserting the positioning pin to complete the operation.

Precautions

Before operating the handwheel, ensure that the process conditions allow valve movement and confirm that the cylinder is connected to avoid air trapping that could damage the actuator.

Under no circumstances should pipe wrenches, torque wrenches, or other tools be used to force the handwheel, as this could damage the valve and actuator.

By correctly mastering the operation methods of handwheel mechanisms, operators can perform manual operations in emergencies, ensuring system safety and stable operation.

Conclusion

Through daily operations and regular inspections, ensuring that pneumatic control valves operate under optimal conditions can significantly improve their stability and service life. Avoiding prolonged operation at small openings, frequent switching, vibrating environments, and overpressure/overtemperature conditions, along with timely issue detection during inspections, can effectively prevent failures. Additionally, mastering the operation methods of handwheel mechanisms provides a safeguard for emergency valve operations, ensuring the safety and stable operation of the process system.