What is a Globe Valve?

A globe valve is a type of linear motion valve used to start, stop, and regulate fluid flow in a pipeline. Its name comes from its globe-shaped body that houses the internal components, although modern designs can vary in shape. Globe valves are critical for regulating the flow, pressure, and direction of fluids and are used across industries such as oil and gas, manufacturing, power generation, and water treatment. This article provides an in-depth overview of globe valves, explaining their functionality, design, and typical applications.

How Does a Globe Valve Work?

Key Components of a Globe Valve

1. Disc: The disc is one of the most vital parts of the globe valve, responsible for throttling, opening, or closing fluid flow. Different disc designs are used for various applications:
   • Plug Disc: This type of disc provides excellent throttling capabilities and is suitable for high-pressure environments.
   • Composition Disc: Contains a non-metallic insert, providing a tight, leakage-free closure, ideal for low-pressure applications.
   • Ball Disc: Typically used for low-temperature and low-pressure applications, providing a balance between throttling and shutoff performance.
2. Stem: The stem connects the disc to the handwheel or actuator, transferring motion to open or close the valve. Depending on the valve design, the stem can be either rotating or non-rotating. A well-designed stem ensures smooth operation and helps maintain a tight seal by minimizing wear on the packing.
3. Seat: The seat is where the disc seals to prevent fluid flow. It is often made of durable materials like Teflon or stainless steel, ensuring reliable isolation and preventing leaks. The seat’s design is crucial for maintaining the valve’s sealing integrity.
4. Bonnet: The bonnet serves as a cover for the valve and provides a leak-tight seal for the valve housing. It also contains the packing, which prevents leakage around the stem.
5. Packing: The packing surrounds the stem and helps prevent leakage from the valve. It is typically made of a wearable material such as Teflon, which may need to be replaced during maintenance.

How A Globe Valve Operates

A globe valve is used to regulate, start, or stop fluid flow. The key components involved in the working of the valve are the handwheel, stem, plug, seat, and body. Below is a step-by-step explanation of its working principle:

1. Manual Operation: The operator turns the handwheel (16), which in turn rotates the stem (11). The stem is connected to the plug (4), also called the disk, which directly controls the fluid flow through the valve.
2. Linear Motion of Stem: As the handwheel is turned, the stem (11) moves vertically, raising or lowering the plug (4) away from or towards the seat (3). When the plug moves away from the seat, fluid is allowed to pass through the valve. Conversely, when the plug is pressed against the seat, it blocks the flow.
3. Flow Control: The guide sleeve (6) helps stabilize the stem during its movement, ensuring smooth operation. The packing (12), located around the stem, ensures that there is no leakage along the stem path, providing a reliable seal.
4. Leak Prevention: The gaskets (2, 7) provide additional sealing between the body (1), bonnet (8), and other components to ensure the valve is leak-tight when in the closed position. The bonnet (8) houses these components and supports the stem and packing assembly.
5. Throttling: Due to its design, a globe valve is ideal for throttling. The plug (4) can be partially lifted from the seat (3), which allows precise control of the flow rate. The double-screw bolts (10) secure the bonnet and prevent leaks under pressure.
6. Closing the Valve: When the handwheel (16) is turned in the opposite direction, the stem moves down, causing the plug to press against the seat. This closes the passage for fluid flow, providing a tight shutoff.

This design allows for efficient control of flow with minimal leakage, making globe valves suitable for applications requiring precise flow regulation. The lock nut (13) ensures that the stem remains in position once the desired degree of valve opening is achieved. The pressing sleeve (14) and plate (15) help maintain the stability and durability of the entire assembly during operation.

Types of Globe Valves

There are several variations of globe valves, each designed for specific applications:

1. T-Type Globe Valve (Z-Type): The most common globe valve design, featuring a straight-through flow path. It offers good throttling capabilities but has a higher pressure drop compared to other designs.

1. Y-Pattern Globe Valve: The Y-pattern design reduces flow resistance, making it ideal for applications where pressure drop is a concern. The stem and seat are positioned at a 45-degree angle to minimize turbulence, making it effective for high-pressure and high-temperature services. This type is often used in scenarios where pressure drop must be kept as low as possible.

1. Angle Globe Valve: This design allows for a 90-degree turn of the fluid, reducing pressure drop and making it suitable for applications where space is limited or piping needs to change direction. Angle globe valves are particularly effective for handling pulsating flows.

Cage-Guided and Double-Ported Globe Valves

1. Cage-Guided Globe Valve: A modern design that uses a piston-shaped plug inside a cage, which helps guide the plug and allows for adjustable flow characteristics. Cage-guided valves provide better stability and smoother operation, making them ideal for high-pressure applications.
2. Double-Ported Globe Valve: This design features two sets of plugs and seats, which helps balance the pressure on either side of the valve. Double-ported valves are easier to actuate due to the opposing force vectors, making them suitable for control applications where tight shutoff is not required.

Advantages and Disadvantages of Globe Valves

Common Applications of Globe Valves

Given their versatility and control capabilities, globe valves are widely used in different industries:

• Oil and Gas: Globe valves regulate the flow of crude oil and natural gas in pipelines, particularly in cooling systems and feedwater systems. For example, they are often used in offshore drilling platforms to control the flow of hydrocarbons and in gas processing facilities to manage process gas streams.
• Water Treatment: They are commonly employed in water distribution systems to control flow and pressure, including in coolant loops and steam lines where precise throttling is required. In wastewater treatment plants, globe valves help regulate the flow in sedimentation tanks and chemical dosing systems to maintain treatment efficiency.
• Power Generation: Globe valves are used in cooling and steam systems to regulate the flow of water and steam. They are also employed in turbine lubrication systems where consistent flow regulation is crucial. For instance, in thermal power plants, globe valves manage the flow of feedwater to boilers and control steam extraction from turbines.
• Chemical Industry: In chemical plants, globe valves control the flow of both corrosive and non-corrosive fluids. They are especially useful in applications where the ability to handle toxic or high-temperature fluids is necessary. For example, globe valves are used to precisely meter chemicals in reaction vessels and to control cooling water flow in exothermic reactions.

Specific Use Cases

• Heat-Conducting Oil Systems: Used as a shut-off valve for heat-conducting oil, toxic, flammable, or radioactive fluid pipelines.
• High-Pressure and High-Temperature Applications: Suitable for use in high-pressure and high-temperature applications like power plants and petrochemical systems.
• Systems Requiring Low Pressure Drop: Y-pattern globe valves are preferred in systems where maintaining a low pressure drop is crucial.
• Viscous Media Limitations: Globe valves are not ideal for high-viscosity media, fluids prone to coking, or pipelines that require full-bore flow.

Conclusion

The globe valve is a critical component in industrial systems where precise control of fluid flow, pressure, and direction is required. With its versatility in regulating flow, effective shutoff capability, and ability to handle both high-pressure and high-temperature applications, the globe valve is a reliable choice for many industries, including oil and gas, power generation, water treatment, and chemical processing. Understanding the various types, actuator options, specific use cases, and maintenance requirements of globe valves allows potential buyers to make well-informed decisions tailored to their operational needs.