Cleaning Methods and Procedures for Pneumatic Control Valves

Pneumatic control valves, such as butterfly valves, are widely used in heating, gas supply, water supply, and other pipeline systems. Especially in power plant heating systems, triple eccentric hard-sealing butterfly valves are often selected. After installing the valve and pipeline, thorough cleaning is required to ensure proper operation. Cleaning the pneumatic control valve is a key step to ensure its long-term stable performance. Common cleaning methods include water flushing, air purging, and steam cleaning. Below are detailed explanations of these three cleaning methods and their applications.

Water Flushing

Water flushing is one of the most commonly used and effective cleaning methods for pneumatic control valves. The main goal is to remove dirt, deposits, and other contaminants from the internal parts of the valve body and pipelines.

Cleaning Requirements and Steps

Water Quality: The water used for flushing must be clean. When flushing austenitic stainless steel pipes, the chloride ion content in the water should not exceed 25 ppm to avoid corrosion of the pipes and valves.
Flow Rate: The water flow rate during flushing should be maintained at 1.5 m/s or higher to effectively flush the interior of the pipeline. Insufficient flow speed may result in incomplete removal of contaminants.
Drainage Requirements: The flushed water must be directed to a reliable drainage system. The drainage pipe's cross-sectional area should be at least 60% of the flushing pipe's cross-sectional area, and negative pressure should be avoided during drainage. All drainage branches must be thoroughly cleaned.
Flushing Standard: Water flushing should continue until the color and transparency of the discharge water match the inlet water, and a visual inspection confirms it is clean. After flushing, if the pipeline is not used immediately, it should be drained and blown dry to prevent residual moisture that could cause corrosion.

Air Purging

Air purging is used to clean pipelines by blowing compressed air, especially in large-scale production facilities, where large compressors are often used for intermittent purging.

Cleaning Requirements and Steps

Purging Pressure and Flow Rate: During purging, the pressure of the compressed air should not exceed the design pressure of the pipeline or container, and the flow rate should not be less than 20 m/s to ensure the air speed is sufficient to carry contaminants away.
Oil-Free Air: The purging air must be oil-free to prevent contamination of the valve and pipeline with oil residues.
Inspection Standard: During air purging, a white cloth or white-painted wooden target board can be placed at the exhaust outlet to visually check for smoke, dust, or other impurities. If no rust, dust, or moisture is found on the target board within 5 minutes, the cleaning is considered successful.

Steam Cleaning

Steam cleaning is suitable for thorough cleaning of large pipeline systems, especially when higher temperatures and flow rates are required during cleaning.

Cleaning Requirements and Steps

Steam Flow Rate and Temperature: When using high-flow steam for cleaning, the flow rate should not be less than 30 m/s to ensure the high-temperature steam can effectively remove contaminants. The temperature and pressure of the steam should be controlled according to the pipeline material requirements to avoid damage to the pipes and valves.
Pipeline Preheating and Drainage: Before steam cleaning, the pipeline should be preheated to ensure uniform temperature and remove any accumulated water that could affect the cleaning effectiveness. The pipeline's thermal displacement should also be checked to prevent deformation or damage due to thermal expansion.
Cleaning Cycle: Steam cleaning typically involves a cycle of heating, cooling, and reheating to ensure thorough removal of contaminants.

Cleaning Steps for Pneumatic Control Valves

In addition to cleaning the pipelines, the pneumatic control valve itself also needs to be cleaned regularly, especially when the valve malfunctions or requires maintenance. Control valves are often contaminated by process fluids, and when the media is corrosive, these contaminants not only affect the equipment's performance but may also pose safety hazards. Therefore, a specialized cleaning method is required to ensure the equipment is restored to normal working condition.

1. Choose Appropriate Cleaning Media

Select the appropriate cleaning medium based on the type and nature of the contaminants. Common cleaning media include water, steam, and acidic or alkaline solutions. In cases of heavy metal contamination, special high-temperature or long-duration treatments may be required.

2. Prepare Cleaning Equipment and Tools

Before cleaning, prepare all necessary equipment and tools, including cleaning containers, heating equipment, steam hoses, and washing devices. Ensure these tools are thoroughly cleaned to avoid secondary contamination.

3. Perform Cleaning Operations

Place the pneumatic control valve components in the cleaning container and use the selected cleaning medium to thoroughly clean the dirt and contaminants. During cleaning, ensure that all parts are evenly cleaned. For stubborn contaminants, longer soaking or treatment times may be necessary.

4. Prevent Secondary Contamination

After cleaning, take care to prevent re-contamination. When reassembling the valve, use clean parts and ensure all cleaning equipment and tools are kept clean. Protective measures such as corrosion-resistant coatings can be applied to prevent future contamination.

5. Safety Operations

The cleaning process should be carried out in a safe environment to ensure that workers are not exposed to potential hazards. When using chemical cleaning agents, proper safety measures should be followed, such as wearing protective clothing and using ventilation equipment.

Conclusion

Cleaning pneumatic control valves is an essential step in ensuring stable and efficient operation of the equipment. Whether cleaning the pipelines or the valve itself, it is crucial to choose the appropriate cleaning method based on the specific situation and follow strict operational procedures. Water flushing, air purging, and steam cleaning each have their unique characteristics and applications. By selecting the proper cleaning method based on actual needs, the service life of pneumatic control valves can be effectively extended, ensuring the safety and efficiency of the system.