Selection Guidance for Globe Valves
Introduction
A globe valve is a type of valve used for regulating or isolating fluid flow in a pipeline. Globe valves have been part of the process industry since the late 19th century and remain a popular choice today. Selecting the right type of globe valve for an application is essential to ensure reliable performance, longevity and cost-effectiveness. A thorough understanding of the different types of globe valve, their key features and the selection criteria will help to ensure the ideal valve for an application is selected.
Classification of Globe Valves
Globe valves are generally classified according to two criteria: control characteristic and end connection.
1. Control characteristics:
Control characteristics refer to the way that the valve controls the flow of fluid through the pipeline. Globe valves are categorized by the type of flow control they provide:
- Linear: Linear valve flow exhibits an almost linear relationship between the open area of the valve and the pressure drop across the valve.
- Equal percentage: This type of globe valve flow exhibits an exponential relationship between the opening of the valve and the pressure drop across the valve.
- Quick opening: Quick opening valves have a much faster opening time than linear or equal percentage valves.
2. End connection:
The end connection refers to the way that the valve is attached to the piping system. Globe valves are available in two end connection types:
- Threaded: This is the most common type of end connection for globe valves.
- Flanged: Flanged globe valves are used in applications that require a higher pressure rating than the piping can support.
Selection Criteria
When selecting a globe valve, consider the following criteria:
1. Application: The application will determine the type of globe valve needed. Consider the systems operating temperature and pressure, as well as the type of fluid being handled. Its also important to take into account the type of control needed (linear, equal percentage or quick opening).
2. Size: Select a valve whose size fits the application. Consider the nominal pipe diameter, end connection type (threaded or flanged) and the pressure rating of the valve.
3. Valve design: The construction material must be able to withstand the systems operating temperature, pressure, and type of fluid. Consider the type of bonnet design (standard or extended), the type of disc (class, plug), and the type of stem packing (graphite or metal).
4. Pressure rating: The pressure rating of the valve must be able to withstand the systems maximum operating pressure.
5. Actuation: Globe valves can be automated with manual, electric or pneumatic actuators. Consider the specific requirements for the intended application.
Conclusion
Selecting the right globe valve for an application is essential to ensure reliable performance and longevity. By understanding the different types of globe valve, as well as their key features and selection criteria, it is possible to identify the ideal valve for an application. Categorizing valve flow control characteristics, end connections and taking into account the application and design of the valve all help to ensure the right globe valve is selected.
