Basic Guide to Bypass Valve Installation for Control Valve

 
The installation of bypass valves for control valves plays a crucial role in industrial production, primarily aimed at ensuring the continuous operation of the production process in case of control valve failures. Bypass valves not only enhance the reliability and flexibility of the system but also provide effective solutions in various complex working conditions. This guide will explore the necessity of bypass valves for control valve, configuration principles, and applicable scenarios, offering practical references for engineers and technicians.

Basic Purpose of Bypass Valves

 
The installation of bypass valves is primarily to maintain production continuity when a control valve malfunctions. Specifically, the establishment of bypass valves is closely related to equipment maintenance needs, fluid characteristics, and safety.

1. Ensure Production Continuity

 
In the event of a control valve failure, the bypass valve can provide an alternate fluid pathway, ensuring that the production system remains operational and preventing economic losses and production delays.

2. Facilitate Maintenance

 
For equipment that does not require frequent shutdowns for maintenance, the installation of a bypass valve can prevent production interruptions. Conversely, for devices that require immediate maintenance, the installation of a bypass valve becomes especially important.

3. Supplement Flow

 
When the flow capacity of the control valve is insufficient, the bypass valve can serve as a supplemental flow measure. Although this approach may affect regulation quality, it remains a viable solution in certain contexts. For example:
 
In steam lines driving standby pumps.
In areas prone to leaks of hazardous media such as hydrogen, phenol, or hydrofluoric acid.
In pipelines carrying slurries where introducing flushing fluid is difficult, the bypass valve can help maintain system stability.
In scenarios where sediment may form in pipelines that do not have continuous fluid flow.

4. Safety Considerations

 
For control valves with a nominal diameter greater than DN80 and of reliable quality, the absence of shut-off and bypass valves does not affect safe operation, ensuring system stability and safety.

Configuration of Handwheels and Bypass Valves

 
When designing control valves, the configuration of handwheels and bypass valves should be considered comprehensively, typically following these principles.
 
With Bypass Valve Present: If a bypass valve is installed, a handwheel is usually unnecessary. The bypass valve can provide fluid flow during a control valve failure, reducing reliance on manual operation.
With Handwheel Present: If a handwheel is installed, the necessity for a bypass valve diminishes, as the handwheel itself allows for manual control and enables operators to make immediate adjustments when needed.

Bypass Valve and Handwheel Configurations in Different Conditions

 
In different operational scenarios, the configurations of bypass valves and handwheels can be flexibly adjusted based on specific needs.

1. Neither Bypass Valve Nor Handwheel Installed

 
Safety Interlocks (SIS): These systems require automatic control under specific conditions and cannot rely on manual operation.
Compressor Anti-Surge Control Valves: Prevent equipment failure and ensure system safety.
Hazardous Areas: Installed in restricted access hazardous areas, requiring strict control to ensure safety.
Operations Where Shutdowns Are Permitted: In such cases, there is no need for a bypass or handwheel to maintain operational flexibility.

2. Bypass Valve Installed but Handwheel Not

 
Timely Replacement or Maintenance of Control Valves After Failure: A bypass valve ensures continued fluid flow, preventing production interruptions.
Control Valves for Continuous Adjustment: During initial production or with significant fluctuations in fluid flow, a bypass valve assists in regulation to ensure stable process operations.

3. Handwheel Installed but Bypass Valve Not

 
Precision Control: For ratio adjustments requiring high-precision operations, a handwheel offers a more flexible adjustment method.
Critical Valves in Sequential Control: The failure of these valves could significantly impact the overall system, necessitating precise control.
Large-Diameter Valves: In cases where a handwheel is required to limit valve opening to prevent excessive opening.

4. Both Bypass and Handwheel Installed

 
In some scenarios, both a bypass valve and a handwheel can be installed. In such cases, priority should be given to installing the handwheel, especially in the following conditions:
Intermittent Operations: Where frequent start-stop operations are required, the handwheel provides immediate adjustment capabilities.
Backup Systems: In case of a failure in the main system, the backup system can immediately take over to ensure production stability.
Leakage Reduction: When handling highly toxic, corrosive, or self-igniting media, the precise control capability of the handwheel can minimize leakage risks.
Sediment Reduction: In processes involving solid particles, slurries, crystallization, or temperature-sensitive polymers, a handwheel can effectively adjust flow and reduce sedimentation probability.
Pressure Differential ≥4MPa: Under high-pressure conditions, increased safety is necessary, and the handwheel can provide more direct control.
Pipe Diameter ≥DN80: Larger pipeline systems require additional control methods, and a handwheel can enhance operational flexibility.
Specialized Control Valves: Control valves designed for specific applications may require more refined control.

Conclusion

 
By reasonably configuring bypass valves and handwheels, the reliability and safety of control valves can be significantly improved, ensuring smooth production processes. During the design phase, it is essential to consider the characteristics of working conditions, equipment functional requirements, and fluid properties to develop the optimal valve configuration scheme. A well-planned valve configuration not only enhances production efficiency and reduces maintenance costs but also optimizes production processes while ensuring safety, ultimately improving overall production effectiveness.