A Complete Guide To What is Globe Valve

Sep. 09, 2024

Globe valves are an essential component for fluid flow management, serving primarily two functions: acting as throttling valves and enabling on-off operations. These versatile valves find applications across various industries including water distribution, turbine sealing, and fuel oil handling.

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However, it is crucial to understand that the globe valve's design can cause fluid flow resistance, resulting in significant pressure drops. Consequently, before choosing a globe valve, attention should be paid to factors like pressure drops at different positions within the valve and the proper sizing of the valve.

This article will delve into the operation of globe valves, their components, installation and maintenance protocols, as well as factors to consider when purchasing an industrial globe valve.

What Is A Globe Valve?

Globe valves are types of valves where the disc or plug moves linearly to allow, restrict, or regulate the flow of media. This linear motion of the disc results in the term "linear motion valves." As the disc descends within the valve, it opens the globe valve seat to permit flow. Their design primarily facilitates throttling and flow regulation; however, they are also effective in on/off control circuits.

During the flow passage through the globe valve, the fluid interacts with the seat and the underside of the valve disc before moving on, effectively cleaning the disc and minimizing dirt accumulation within the valve body. Nevertheless, this process alters both the flow rate and direction, leading to a considerable pressure drop in the flow.

Globe Valve Symbol

The symbol representing a globe valve consists of two triangles converging at a point, with a solid circle placed at their intersection and horizontal lines extending outward. These horizontal lines indicate that a globe valve functions as a two-way inline valve, versatile in throttling and on-off applications.

The globe valve symbol used in piping and instrumentation diagrams (P&ID) is a variant of the standard valve symbol but lacks the solid circle at the convergence point of the triangles. The isometric symbols depicted in the diagram signify connections for butt-welding, flanged ends, and socket ends.

Types of Globe Valves

Globe valves come in various types, categorized based on their body design and the connection between the body and bonnet.

Based On Valve Body Design

Based on their body configurations, globe valves can be classified into three types: Angle pattern, Standard or T-pattern, and Oblique or Y-pattern globe valves.

Standard Pattern (T-Pattern) Globe Valve

This commonly used industrial valve features a horizontally set seat that causes the disc to move perpendicularly to the flow through the pipe flanges. The standard pattern globe valve experiences several obstructions within the body, resulting in significant pressure drops during fluid passage.

Utilized in extreme throttling applications, the T-pattern globe valve is well-suited for processing plants, particularly around control valves, and in operations where fluid pressure losses are less critical.

Angle Pattern Globe Valve

This type is a modified version of the T-pattern, designed with its ends at a right angle, causing fluid to flow after a 90-degree turn. Angle pattern globe valves provide a higher flow coefficient compared to their standard counterparts.

The design is adept at handling slug flow, making it ideal for fluids with variations and pressure fluctuations. Placing angle pattern globe valves close to pipeline ends helps reduce the number of required pipe joints and serves as an elbow for directing fluid flow.

Oblique Pattern (Y-pattern) Globe Valves

Among the globe valves, the oblique pattern exhibits the least resistance to fluid flow, resulting in minimal pressure drops. The seat is positioned at a 45-degree angle to the stem, which promotes direct fluid flow and elevates efficiency.

Not easily subject to erosion, Y-pattern globe valves excel in flow regulation and can effectively flush out sludges when operating in closed lines, making them advantageous over other types.

Based On Body-Bonnet Connection

The bonnet of a globe or gate valve is located atop the valve body and connects it to the actuator or manual lever device, allowing access to internal components for maintenance.

Manufacturers typically design bonnets to be detachable from the body, facilitating maintenance and ensuring the integrity of the seal.

Bolted Bonnet Connection

The bolted bonnet globe valve, or screwed-in type, represents the most economical option for connection. However, frequent uncoupling may risk damaging the area around the bolts due to the torque required. This connection is primarily used for smaller valve sizes.

Welded Bonnet Connection

By welding the bonnet onto the valve body, the welded bonnet globe valve achieves durability across different sizes and operational conditions. However, once welded, uncoupling poses a risk of damaging either the bonnet or the valve body.

Flanged Bonnet Connection

This type features bolts spaced throughout the connection area, enhancing the grip compared to bolted connections and enabling use with various valve sizes and demanding operational environments. For larger sizes, a welded flanged connection may be employed for added safety.

Union Ring Bonnet Connection

In this configuration, the bonnet connects to the valve body via a union ring, minimizing wear from disassembly. However, this design typically caters to smaller valve sizes.

Pressure Seal Bonnet Connection

This type is engineered for high temperature and pressure situations, utilizing fluid pressure to tighten the bond between the bonnet and body.

Globe Valve Advantages and Disadvantages

When comparing globe valves to other types such as ball and gate valves, it's important to note that globe valves primarily serve as throttling devices, offering several advantages in piping operations:

Advantages

Good Throttling Ability

The vertical motion of the valve disc against the valve seat enhances the globe valve's throttling performance. As the valve closes, the distance between the disc and seat decreases, enabling effective flow regulation.

Maintenance and Structure

Thanks to their simple construction—with one sealing surface and minimized sealing area—globe valves are cost-effective and easier to maintain compared to gate valves.

In terms of production processes, less material is needed, translating into lower construction costs.

Good Sealing Performance

Due to minimal sliding between the sealing surfaces, there is reduced friction and wear, promoting long-lasting sealing capabilities.

Moreover, the durability of the sealing surfaces leads to an extended service life compared to other valve types.

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Other advantages of the globe valve include:

Installation does not have significant height requirements due to the valve's robust structure.
Availability of various designs caters to broader valve selection.
Reduced seat leakage in comparison to gate valves.

Disadvantages

While globe valves have their merits, they also come with certain drawbacks:

Large Torque Requirements

The need for substantial torque arises as the valve disc faces the fluid pressure from the opposite end. This necessity extends to both closing and opening the globe valve.

High Flow Resistance And Pressure Losses

Globe valves exhibit the highest flow resistance due to the multiple obstructions in the valve body, resulting in considerable pressure losses.

Restricted Flow Direction (Unidirectional)

Globe valves facilitate fluid flow only in one direction, meaning fluids can only progress vertically without altering direction.

Other disadvantages include:

Complex installation processes.
Requirement for large openings to accommodate the disc.
Generally power-consuming and may produce noise during operation.

Globe Valve Functions

Globe Valves function effectively both as on-off isolation valves and for throttling purposes in media regulation. Designed primarily for flow regulation, they also serve critical roles in fully blocking or enabling fluid flow.

Due to their compact height compared to gate valves, the disc of a globe valve travels a smaller distance to engage the valve seat. This design facilitates throttling operations by slowly diminishing the gap between the valve seat and disc.

Also, the globe valve is less prone to damage during partial opening due to its structural design, enhancing its effectiveness as a throttling device.

In the context of on-off operations, careful selection of the disc design maximizes sealing reliability. Linear motion valves, inclusive of gate, needle, and globe valves, are applicable across diverse operational settings under suitable conditions.

Globe Valve Parts

The essential components of a globe valve include the actuator, stem, disc, body, seat, and bonnet.

Globe Valve Disc

The disc serves as the main element regulating fluid flow. Its motion up or down corresponds with the rotation of the stem.

Disc designs can vary and include the plug, composition, and ball disc types.

Plug Disc Design

Characterized by a narrowing end leading to a flat surface, this design excels in flow regulation.

Composition Disc Design

Recommended for water systems, these discs resist erosion and come with replaceable options due to their broader surface area.

Ball Disc Design

This type is mainly suited for on-off applications and performs best under lower temperature and pressure conditions.

Globe Valve Seat

The valve seat acts as a sealing surface for the disc, which may either be integrated with the valve body or screw-in. When the disc descends to close the valve, it meets the seat at a right angle, ensuring a robust seal.

A globe valve back seat serves as the sealing point for the connection above the disc, with the intention to prevent media pressure from affecting the valve packing while the valve is open.

Globe Valve Stem

The stem connects the valve disc to the actuator, often affixed to the bonnet. The disc may attach to the stem through a slipping or screw mechanism, promoting rapid closure.

Globe Valve Body

This structure safeguards the internal components and is designed for simple yet robust construction.

Globe Valve Actuator

The actuator rotates the stem, thereby controlling the disc movement. Open and close actions hinge on the actuator type, which may be either:

Manually Operated Actuators: Utilizing hand wheels or cranks for control.
Automatically Operated Actuators: Employing electric, pneumatic, or hydraulic systems for operation.

Globe Valve Bonnet

Located atop the body, bonnets serve the role of connecting the actuator to the valve body while allowing space for the stem to pass through.

How Does The Globe Valve Work?

The primary purpose of a globe valve is to regulate, allow, or restrict flow through the pipe system. This is accomplished with the aid of the valve's disc and seat.

The seat is positioned parallel to the center of the pipe enabling effective sealing. Upon operating the actuator or turning the handwheel, the valve disc moves accordingly.

During on-off operations, the disc lowers completely onto the seat for sealing or rises entirely to permit maximum flow. For throttling, the disc is only partially raised, correlating flow with the extent of disc elevation.

Installation and Maintenance Of Globe Valves

Installation

Proper installation is vital to reduce premature wear and enhance valve operation. Best practices include upright positioning, waste removal, and adherence to specific guidelines:

Ensure internal areas are free from fluids before fitting.
Provide support to the valve load to prevent damage.
Facilitate adequate space for valve installment.
For flanged connections or bolts, tighten them diagonally.
Test bolt integrity by increasing pressure within the valve.
Inspect valve component materials for travel damage.
Confirm the pressure rating aligns with operating conditions.
Clean pipe flanges before connecting them to the valves.

Maintenance

Regular maintenance is crucial for the longevity of globe valves, ensuring they operate optimally. Maintenance recommendations include:

Routine inspections to identify and resolve leaks promptly.
Regular cycling of valves when idle.
Cautious adjustment of gland bolts to avoid damages.

What To Consider Before Buying Globe Valves

The selection of globe valves should depend on operational parameters such as temperature, pressure, and fluid type. Critical considerations include valve size, material composition, pressure rating, and design, ensuring an appropriate match for intended uses.

Material

Given their widespread industrial applications, globe valves are produced from diverse materials like cast iron, steel, and plastics. It’s key to understand the characteristics of the media flowing through the valve.

Valves made from stainless steel are generally earmarked for high-temperature applications owing to their resilience against galling and seizing. Consulting manufacturers can provide insights into suitable valve types under specific conditions.

Design

Design classifications cover both the body and the disc of the globe valve. Body designs feature standard, angle, and oblique patterns—each with varying capacities for flow restriction. Disc designs comprise composition, plug, and ball variants that may best serve diverse applications.

Valve Sizes

Proper valve sizing is crucial for ensuring effective throttling capabilities, significantly influencing fluid dynamics. Research and knowledge of requirements are imperative when selecting sizes, as manufacturing typically facilitates sizing based on buyer specifications.

The role of valve size can differ based on operational needs. In throttling situations, size plays a vital role in determining pressure drops at specific points. Conversely, in on-off functions, although pressure drop assessment may not be critical, smaller sizes can be economically favorable.

Standards

Common standards applicable in the petrochemical sector for globe valves include:

BS: cast steel valves
API 603: stainless steel valves
API 602/BS: forged steel valves
API 598 and BS EN-1: valve testing guidelines
ASME B16.10: face-to-face dimension standards
ASME B16.5 and ASME B16.47: standards for flanged connections
ASME B16.25: butt weld connection design guidelines

Conclusion

This article explored the functionalities of globe valves, their components, installation and maintenance best practices, and considerations to keep in mind when selecting an industrial globe valve.

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