What Is a Globe Valve

Figure 1: A pneumatic globe valve

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A globe valve is a type of valve used to start, stop, and/or regulate flow in a pipeline. The valve has a movable disk-type element and a stationary ring seat within the valve body and it is effective in throttling flow and allowing for precise control. The name globe valve is from its spherical body shape. This article explores the working mechanism, features, and common applications of globe valves.

Table of contents

Globe valve parts and working principle

A globe valve has two separate chambers for flow control. The actuation process involves rotating a stem via a handwheel or mechanical actuator, which in turn, lifts or lowers the plug or disc. The globe valve working principle is explained in detail below:

• Movement of the disc: The core mechanism of a globe valve involves the movement of a disc (or plug) (Figure 2 labeled C) in relation to the stationary ring seat. The disc is connected to a stem (Figure 2 labeled A) which is, in turn, operated by an external actuator (manual, using a handwheel, or automatic, using pneumatic, hydraulic, or electric actuators). When the handwheel or actuator is turned, it moves the stem and the attached disc in a linear motion towards or away from the seat.
• Flow regulation: In the open position, fluid flows through the space between the disc and the seat. As the valve closes, the disc moves towards the seat, gradually reducing the flow area and thereby restricting the flow. When the disc fully contacts the seat, the flow is completely stopped. This precise control over the disc position allows for excellent throttling capabilities, making the globe valve ideal for flow regulation.
• Sealing mechanism: The seat is usually designed to match the shape of the disc for a better seal. In some designs, the disc may be composed of or coated with a softer material to ensure a tighter seal.

Figure 2: Globe valve diagram showing the various globe valve components: A globe valve in the open position (left), and in the closed position (right) showing stem (A), bonnet (B), disc or plug (C), and valve body (D).

Globe valve advantages

• Exceptional throttling and modulation: Globe valves are ideal for precise flow control, allowing fine adjustments to flow rate, which is crucial in systems requiring regular modulation.
• Reliable shutoff capability: They ensure a tight seal when closed, critical for stopping flow during maintenance or emergencies.
• Maintenance and repair efficiency: Designed for easy maintenance, their components are readily accessible, reducing downtime and costs.
• Versatility in maintenance: The disc and seat can be replaced or resurfaced, prolonging valve life and ensuring efficient operation.

Globe valve disadvantages

• Significant head loss: One major disadvantage of globe valves is the pressure drop due to the fluid's path through the valve, which can be mitigated by using Y-shaped or angle globe valves for less turbulence and pressure loss. The head loss should be considered while designing globe valve flow parameters.
• Increased operating force: More force is required to operate globe valves, especially in high-pressure settings, often necessitating automated actuators.
• Slower operation: Their design is not suited for situations requiring quick opening or closing due to the multi-turn operation.
• Susceptibility to cavitation and flashing: High-pressure differentials can cause cavitation and flashing, potentially damaging the valve.
• Cost: The complex design and manufacturing process make globe valves more expensive compared to other valve types.

Applications of globe valve

Globe valves are the optimal choice for applications requiring precise flow modulation, where pressure loss is not a critical concern, including scenarios such as:

• Cooling water systems
• Fuel oil systems
• Feedwater and chemical feed systems
• Boiler and main steam vents and drains
• Turbine lube oil system
• Drain and trim applications in sprinkler systems (not as control valves in fire sprinkler systems, where pressure is at a premium)

Read our globe valve applications article for more information on the industrial applications of globe valves.

Globe valve design variations

Flow path design

Globe valves have multiple designs based on their flow path:

1. T- or Z globe valve (Figure 3 left): This is the most common design for globe valves, characterized by a body that forces the flow to change direction twice, creating a path that resembles the letter "Z." This design is effective for throttling because the seat and disc configuration allows for precise control over the flow. However, this design also results in a higher pressure drop across the valve with a typical L/D coefficient of ~340.
2. Angle globe valve (Figure 3 middle): As the name suggests, angle globe valves have a body designed so that the inlet and outlet ports form a 90 degree angle, resembling an elbow. This design allows the fluid to change direction only once, reducing the pressure drop compared to the T- or Z-shaped design. 90 degree globe valves are useful in applications where the piping configuration requires a change in direction, combining the functions of a valve and an elbow. These globe valves have a typical L/D coefficient of ~55.
3. Y-globe valve (Figure 3 right): The Y-globe valve is a variation of the standard globe valve designed to minimize the pressure drop. In this design, the valve body and the seat are angled in a way that offers a more direct flow path (less tortuous than the Z-shaped path) while still allowing for good throttling capabilities. The "Y" shape reduces the severity of the flow direction change, resulting in lower pressure loss compared to the traditional T- or Z-shaped globe valves. These globe valves have a typical L/D coefficient of ~150.

Additionally, double-seated globe valves feature two plugs and corresponding seats, enhancing their capability to handle higher flow rates and providing a balanced design that minimizes the force required to operate the valve, making them an efficient choice for applications requiring precise flow control with minimal actuation force.

Figure 3: T- or Z globe valve (left), angle globe valve (middle), Y-globe valve (right)

Plug design

Globe valves can have one of the following plug designs:

1. Plug disc: The plug disc design is characterized by its solid, tapered shape, which fits snugly into the valve seat to regulate or block flow. This type is known for its durability and effectiveness in providing a tight seal, making it suitable for applications requiring precise flow control.
2. Composition disc: Featuring a disc with a replaceable insert, usually made of a softer material like rubber or PTFE, the composition disc is designed to ensure a tight seal even in the presence of particulate matter in the fluid. This type is ideal for applications where sealing against impurities is critical.
3. Ball disc: As the name suggests, this disc type incorporates a spherical ball that aligns with the seat to control flow. The ball disc offers smooth operation and is particularly effective in applications requiring quick shutoff capabilities. Its design allows for easy maintenance and is suitable for moderate control applications.

Figure 4: Globe valve disc types: Plug disc (left), composition disc (middle), and ball disc (right)

Globe valve flow characteristics

Globe valves exhibit distinct flow characteristics that are pivotal in their selection and application in fluid control systems. These characteristics are primarily defined by the valve's inherent flow coefficient (Cv), flow curve, and the relationship between the valve lift and flow rate under varying pressure conditions.

Inherent flow coefficient (Cv)

The globe valve Cv value represents the valve's flow capacity, indicating the volume of fluid that can pass through with a one psi pressure drop. Globe valve flow coefficient is typically low due to their design, which prioritizes precise flow control over high flow capacity.

Flow curves: linear vs equal percentage

• Linear flow curve: Offers a direct proportion between valve lift and flow rate, suitable for applications with constant pressure drop.
• Equal percentage flow curve: Provides an exponential relationship between valve lift and flow rate, ideal for varying pressure drop conditions, enhancing control precision.

Proper sizing is crucial to match the valve's flow characteristics with the application's requirements, ensuring efficient operation. The choice between linear and equal percentage depends on the system's pressure dynamics and control needs.

Figure 5: Globe valve P&ID symbol

How globe valves compare with other valve types

Other multi-turn/linear motion valves and quarter turn/rotary valves are common valve classifications that are comparable to a globe valve. Their purpose and function determine how they are used in different applications.

Multi-turn/linear motion valves

Industrial globe valves are multi-turn valves. A gate valve also uses a multi-turn handwheel to move the valve plug in a linear direction, but a gate valve has a straight-through flow. The valve stem on a gate valve lowers a plug or obstruction that blocks the path of flow or allows flow without requiring the medium to change direction. Consequently, gate valves have a much lower head loss (L/D=~8) when fully open, but they shouldn&#;t be used to regulate flow due to a drastic increase in head loss and increased wear on the gate valve&#;s gate and seat. Read our globe valve vs gate valve article for more details.

Quarter turn/rotary valves

A rotary valve uses a wrench handle, moving only a quarter-turn (90 degrees) to open or close the valve. The cut-off valve on a gas line is a common example of this type of valve, designed for a quick on/off function. Two common types of quarter turn/rotary valves are ball valves and butterfly valves.

• Ball valves use a sphere, or ball, with a hole bored through it, allowing flow when the hole is parallel to the direction of flow and blocking it when in a perpendicular position.
• A butterfly valve uses a thin plate to block flow when its surface is perpendicular to the direction of flow or allow flow when parallel.

Quarter turn/rotary valves have very low head loss (L/D=~3) but have limited throttling capability. Read our globe valve vs ball valve article for more details.

FAQs

How do you choose between 2 way and 3 way globe valves?

Use 2 way globe valves for on/off or throttling in a single flow path. Use 3 way valves for mixing or diverting flow between two different paths.

How do high-pressure globe valves manage to withstand high pressures?

High-pressure globe valves are designed with robust materials and thicker walls, and often feature a strengthened closure mechanism.

What is the purpose of a position indicator on a globe valve?

A position indicator visually shows the valve's open or closed status, aiding in manual checks and system monitoring.

What are the advantages of using an electric globe valve compared to a manual one?

Electric globe valves offer remote control and automation, allowing for precise flow regulation and easier integration into control systems compared to manual valves.

Table of Contents

1. Introduction to Globe Valves
2. Types of Globe Valves
3. Advantages of Globe Valves
4. Applications of Globe Valves
5. Conclusion & FAQs

Globe valves, an essential component in the world of fluid control, stand as a testament to the sophistication and precision required in modern industrial and residential applications. This comprehensive guide delves into the intricacies of globe valves, covering their design, operation, types, advantages, applications, and much more. Whether you're a seasoned engineer, a maintenance professional, or simply someone keen on understanding the mechanics behind fluid control, this article promises to equip you with in-depth knowledge and insights about globe valves.

Introduction to Globe Valves

Globe valves are a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body. They are named for their spherical shape with the two halves of the body being separated by an internal baffle. This design is what primarily sets globe valves apart from other valve types.

How Globe Valves Work

At the heart of a globe valve's operation is its ability to restrict or permit the flow of a medium. When the valve is opened, the disk moves away from the seat, allowing fluid to pass through the valve. Conversely, when the valve is closed, the disk comes into contact with the seat, effectively halting fluid flow. This simple yet effective mechanism is what makes globe valves highly reliable and efficient in controlling fluid flow.

Key Components

Body: The main structure, often spherical, which houses the internal components.

Disk: The element that moves to open or close the valve.

Seat: A stationary ring that forms a seal with the disk to stop fluid flow when the valve is closed.

Stem: Connects the disk to the actuator or handwheel and transmits motion to open or close the valve.

Bonnet: The cover for the opening in the body through which the stem passes.

Component Interaction

Disk and Seat: The core of a globe valve's functionality lies in the interaction between the disk and the seat. The disk is precision-engineered to fit snugly against the seat, creating a seal that prevents fluid flow when closed. The degree to which the disk is lifted from the seat controls the flow rate, allowing for fine-tuned regulation of fluid passing through the valve.

Stem Movement: The stem, connected to the disk at one end and an actuator or handwheel at the other, translates rotational motion into linear motion. This movement is crucial for the precise positioning of the disk. The stem's design, often threaded, allows for minute adjustments to the disk's position, facilitating accurate control over flow and pressure.

Operation Mechanism

The operation of a globe valve is governed by the movement of the disk in relation to the seat. This movement is typically achieved through a turning mechanism, such as a handwheel or an actuator, which moves the stem and the attached disk. As the handwheel is turned, the stem moves vertically, raising or lowering the disk. This precise control over the disk position allows for the modulation of flow rates, making globe valves ideal for throttling applications.

Flow Characteristics

Globe valves exhibit superior throttling capabilities due to their design. The flow path through a globe valve involves a change in direction, which results in a higher resistance to flow. This characteristic, combined with the precise control over the disk position, allows for effective regulation of flow.

Change in Direction: As fluid enters the valve, it undergoes a directional change, which inherently increases resistance and helps in reducing flow speed. This characteristic is advantageous for throttling as it enhances the valve's ability to modulate flow accurately.

Pressure Drop: The design of globe valves inherently causes a pressure drop across the valve. While this might be a disadvantage in applications where pressure conservation is critical, it is this feature that contributes to the valve's precise control capabilities, especially in regulating flow and reducing velocity.

The operation of globe valves embodies a balance between simplicity and precision, offering robust solutions for controlling fluid flow. Their design principles&#;centered around the interplay between the disk, seat, and stem&#;enable precise flow regulation, efficient throttling, and reliable sealing. By understanding the detailed mechanics and flow dynamics at play, one can appreciate the critical role globe valves serve in various industrial applications, highlighting their significance in modern fluid control systems.

Types of Globe Valves

Globe valves are designed to regulate flow in a pipeline, offering precise control through their various configurations. The diversity in types allows for their application across a broad spectrum of pressures, temperatures, and flow conditions. Here are the main types of globe valves, characterised by their body design, disc type, and flow patterns.

T-Pattern (or Through-way) Globe Valves

Description: Similar to the Z-body in flow path, the T-pattern globe valve features a straight-through flow path but with a different body and bonnet design. This configuration is used when a more traditional globe valve design is required but with a minimal pressure drop.

Applications: Employed in applications needing throttling and where flow direction does not need to be changed.

Guide To Gate Valve Problems and Troubleshooting

Angle Globe Valves

Description: In angle globe valves, the inlet and outlet ports are at a 90-degree angle, changing the flow direction only once. This design reduces the pressure drop slightly more than the Z-body and is efficient for applications involving slurry or viscous fluids.

Applications: Suitable for throttling services and where the flow direction needs to be changed.

Other Types

Suggested reading:
What is the difference between a globe valve and a bellow seal globe valve?

Want more information on 3 globe valve? Feel free to contact us.

Z-Body Globe Valves: Named for its Z-shaped partition inside the valve body, it allows for a straightforward flow path through the valve. This design minimises the resistance and pressure drop across the valve.

Y-Body Globe Valves: Y-body globe valves have a stem and seat angled at approximately 45 degrees to the pipe axis, which offers a straighter flow path through the valve. 

Bellows Sealed Globe Valves: Equipped with a bellows seal in addition to or instead of the traditional gland packing, these valves offer an extra layer of sealing to prevent leakage of the fluid.

The diversity in globe valve types underscores their adaptability and efficiency in various applications. From Straight to Angled Globe Valves, the selection of a globe valve type depends on the specific requirements of the application, including the nature of the fluid, pressure, temperature, and desired flow control. Understanding these types helps in selecting the most appropriate globe valve, ensuring optimal performance, longevity, and safety in fluid handling systems.

Advantages of Globe Valves

Precision in Control

One of the standout features of globe valves is their exceptional capability for precise flow control. The design of the globe valve, particularly the relationship between the disc and the seat, allows for fine adjustments to the flow rate. This precision is essential in applications where the exact control of flow, pressure, or temperature is critical to process efficiency and safety. The ability to modulate flow with high accuracy makes globe valves invaluable in systems requiring meticulous management of fluid dynamics.

Reliable Leak Prevention

Globe valves are designed to provide a tight seal when closed, significantly minimising the risk of leaks. The disc and seat configuration ensures that when the valve is in the closed position, the potential for fluid to pass through is greatly reduced. This leak prevention capability is particularly important in applications dealing with hazardous or expensive fluids where containment is paramount. The enhanced sealing properties of globe valves contribute to safer operational environments and reduced material loss.

Versatility Across Applications

The adaptability of globe valves to various media and operational conditions is another key advantage. They can be used with a wide range of fluids, including water, steam, gas, and oil, as well as in systems handling corrosive or viscous substances. Additionally, globe valves can operate effectively under high pressure and temperature environments, making them suitable for a diverse array of industrial applications, from chemical processing to power generation and beyond.

Ease of Maintenance

Globe valves are engineered for durability, but when maintenance is required, their design facilitates straightforward repairs. Many globe valves are constructed to allow for easy access to internal components, such as the disc and seat, enabling quick replacements or adjustments without the need for complete valve removal from the pipeline. This ease of maintenance helps reduce downtime and operational costs, ensuring smoother, more reliable system performance.

The advantages of globe valves&#;ranging from their precision and reliability in flow control to their versatility and ease of maintenance&#;underscore their importance in fluid management systems. Whether for regulating flow in a high-pressure gas pipeline or managing water distribution in a municipal supply network, globe valves offer solutions that are efficient, safe, and sustainable. Their enduring presence in industrial applications is a testament to the value they bring to operations requiring controlled fluid dynamics.

Applications of Globe Valves

Water Treatment and Distribution

In water treatment facilities and distribution systems, globe valves are used to regulate the flow and pressure of water. They are essential for maintaining the correct water pressure in pipelines, controlling the flow rate during treatment processes, and ensuring the safe and efficient distribution of potable water to residential and commercial areas.

Steam Systems

Globe valves are particularly suited for steam control applications due to their ability to handle high temperatures and pressures. They are commonly found in boilers, steam engines, and steam heating systems, where precise control over steam flow is necessary to maintain efficiency and safety. Their capacity to throttle flow and shut off steam completely makes them indispensable in these settings.

Chemical and Petrochemical Industries

The chemical and petrochemical sectors rely on globe valves for the controlled flow of chemicals, solvents, and other fluids. These industries require valves that can withstand corrosive substances, high pressures, and temperatures. Globe valves, especially those made from materials resistant to corrosion and chemical degradation, are widely used for dosing, mixing, and controlling the flow of aggressive chemicals.

Oil and Gas Production

In oil and gas production, globe valves play a crucial role in controlling the flow of crude oil, natural gas, and related products. They are used in upstream, midstream, and downstream operations for tasks such as regulating pipeline flow, managing pressure in wells, and controlling the delivery of oil and gas to processing facilities and storage tanks.

Power Generation

Globe valves are critical components in power generation plants, including those that use fossil fuels, nuclear energy, and renewable resources. They regulate the flow of steam, water, and other fluids in turbines, cooling systems, and feedwater lines. Their precision and reliability ensure the efficient and safe operation of power generation facilities.

The applications of globe valves are as varied as they are critical, spanning industries that impact virtually every aspect of modern life. From ensuring the safe and efficient operation of water and energy systems to supporting the production of pharmaceuticals and the operation of complex machinery in aerospace, globe valves play an essential role. Their ability to precisely control flow and pressure, combined with their durability and adaptability, makes them indispensable in numerous industrial and commercial applications.

Conclusion

Globe valves play a pivotal role in the control and management of fluid flow across various industries. Understanding their design, operation, and applications is crucial for professionals involved in the specification, maintenance, and operation of fluid control systems. With their ability to provide precise flow control, coupled with durability and versatility, globe valves continue to be an indispensable component in fluid management. As technology advances, we can expect to see even more efficient and environmentally friendly globe valve solutions, further solidifying their position in the industry. Remember, selecting the right globe valve and adhering to proper maintenance practices are key to maximising performance and longevity in any application.

FAQs

What is the primary function of a globe valve?

The primary function of a globe valve is to regulate fluid flow in a pipeline. It can be used to start, stop, and throttle (control) the flow of a fluid, allowing for precise control over flow rate, pressure, and temperature within a system. The unique design of a globe valve, with its spherical body and movable disc, enables it to provide superior flow regulation compared to other valve types.

How does a globe valve differ from other types of valves?

Globe valves differ from other valves in their design and operation. They have a spherical body with a baffle that splits the interior into two halves, and a movable disc or plug that moves perpendicular to the seat to open or close the valve. This design allows for precise flow control and makes globe valves particularly suitable for throttling applications. In contrast, gate valves are better for on/off control without flow restriction, and ball valves offer a balance between flow control and minimal flow resistance.

Can globe valves be used for both liquid and gas applications?

Yes, globe valves are versatile and can be used for controlling both liquid and gas flow. They are effective in applications involving water, steam, oil, gas, and even certain corrosive or viscous fluids. The material of the globe valve and its sealing components are selected based on the specific media and operating conditions to ensure compatibility and longevity.

What are the main advantages of using a globe valve?

Globe valves offer several advantages, including precise control over flow, reliable leak prevention due to tight sealing, versatility across a wide range of applications, ease of maintenance, enhanced safety features, energy efficiency, and durability. These benefits make globe valves a preferred choice in industries where fluid flow needs to be accurately managed.

How do I choose the right globe valve for my application?

Choosing the right globe valve involves considering several factors, including the type of fluid (its temperature, pressure, and corrosive properties), the specific control requirements (such as the need for throttling), the valve material compatibility with the fluid, and the operating environment (temperature and pressure conditions).

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