The common problems and analyses in the application of control valves are as follows: 

I. Selection and Installation Issues 

1. Incorrect selection: 

There are a wide variety of control valves, with numerous specifications and parameters. Incorrect selection can lead to inconvenient installation, maintenance and management. 

When selecting the type, factors such as process conditions, medium properties, pressure, and flow rate should be taken into account to ensure that the control valve can meet the actual requirements. 

2. Installation Issues: 

Improper installation will affect the performance and service life of the control valve. 

When installing, make sure that the control valve is tightly connected to the pipeline without any leakage, and that the installation direction is correct. 

II. Reliability Issues 

1. Increase in leakage rate: 

The characteristics of the control valve at the time of manufacture differ significantly from those after it has been in operation for some time. One of the common problems is an increase in leakage. 

An increase in leakage volume may lead to problems such as a decrease in system pressure and unstable flow. 

2. Increase in noise: 

Control valve noise has become one of the main noise sources in industrial equipment. Reducing control valve noise is currently an important research topic. 

Increased noise levels may affect the working environment and the health of personnel. 

3. Decrease in valve reproducibility: 

A decrease in the repeatability of the valves may lead to a deterioration in the quality of the control system, thereby affecting the stability of the production process and the quality of the products. 

III. Maintenance and Management Issues 

1. Difficulty in maintenance: 

The control valve is heavy, which causes inconvenience in transportation, installation and maintenance. 

During maintenance, mechanical equipment needs to be used, which increases the maintenance cost and difficulty. 

2. Inconvenient management: 

The control valves come in a wide variety of types and specifications, which causes inconvenience in management. 

It is necessary to establish a complete management system to ensure that the selection, installation and maintenance of control valves are properly managed. 

IV. Flow Characteristics Matching Issue 

1. Inconsistent flow characteristics: 

The ideal flow characteristics of the control valve have been determined during the product manufacturing process, but the characteristics of the controlled objects in industrial processes vary. 

Incompatibility of flow characteristics may lead to deterioration of control system performance, thereby affecting the stability of the production process and the quality of the products. 

V. Specific Fault Issues 

1. Internal leakage: 

The valve fails to operate or operates inadequately, resulting in internal leakage. 

The possible causes may include wear of the valve core and valve seat, insufficient force exerted by the actuator, and wear of the valve seat threads, etc. 

2. Large fluctuations in opening degree: 

The significant fluctuations in the opening degree of the control valve affect the stability of the system. 

The possible causes may include locator failure, DCS failure, control cable failure, etc. 

3. Occurrence of the "Casement" phenomenon: 

The control valve is stuck, causing it to fail to operate normally. 

The possible causes may include valve body failure, cylinder failure, pneumatic component failure, etc. 

4. The action is normal but the flow rate remains unchanged: 

The control valve is functioning properly but the flow rate remains unchanged. This might be due to a mismatch in flow characteristics or a fault in other parts of the system. 

VI. Solutions and Recommendations 

1. Strengthen the management of product selection: 

Select the appropriate type based on factors such as process conditions and medium characteristics to ensure that the control valve can meet the actual requirements. 

2. Improve installation quality: 

Strengthen the management of the installation process to ensure that the control valve is tightly connected to the pipeline without any leakage, and that the installation direction is correct. 

3. Strengthen maintenance and upkeep: 

Establish a complete maintenance and upkeep system, and conduct regular inspections, cleaning, lubrication, and other maintenance tasks on the control valves. 

4. Optimize traffic characteristics: 

Optimize the flow characteristics of control valves based on the characteristics of the controlled objects in industrial processes, thereby improving the quality of the control system. 

5. Adopt intelligent valve positioner: 

The intelligent valve positioner has intelligent functions such as self-diagnosis and remote communication of operating status. It enables convenient modification of the flow characteristics of the control valve, thereby enhancing the control accuracy and stability of the control system.