Globe Valves vs. Gate Valves
Gate valves and globe valves both serve important roles in applications that require control of liquid and media passing through industrial systems. As the most common valves used in industrial plants, they are often used in the same applications and are very similar in appearance, but they have different functionalities.
It is important to understand these differences when deciding what valve type to use in your application. This article discusses the differences between and the purposes of each type of valve.
Globe Valves
At a glance, it is easy to understand why globe valves were named as such. Traditional globe valves closely resemble a globe. Belonging to the linear motion valve family, globe valves are primarily intended to start, stop, and regulate the flow of media. Most globe valves have a top-entry design, meaning you have to access the valve’s internal components from the top.
Globe valves provide a tight, efficient seal to limit the risk of leakage. They are suitable throttling valves because their seats are parallel to the media flow, preventing erosion of the seat when the valve is on. Globe valves experience high-pressure drops and are more resistant to media flow when the valve is turned on.
Applications that encounter high temperatures, high pressures, or highly viscous media call for globe valves. They are appropriate for applications that require a safe, leak-proof solution that resists corrosion. Due to their capabilities, globe valves are more costly than gate valves but are a worthwhile expense in certain applications.
Gate Valves
As part of the shutoff valve family, these linear valves feature a wedge-shaped gate and a rising or non-rising stem to indicate when the valve is open or closed. The primary function of gate valves is to isolate media by providing a tight seal to stop the flow. Unlike globe valves, they don’t regulate the flow of media, but they can accommodate any flow direction.
Gate valves are ideal for applications that require tight sealing. Knife valves, a unique variety of gate valves, are suitable for viscous media. Gate valves are useful in wide variety of above- and below-ground applications and are suitable for all kinds of fluids, including gas and water.
Differences: Globe Valves vs. Gate Valves
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While they appear similar in design and can be used in similar ways, these two valves differ in functionality, structure, sealing capabilities, and application.
Some of the most distinct differences between globe valves and gate valves include the following:
Performance/Functionality:
Globe valves are control valves, meaning they can start, stop, and regulate media, giving the operator full control media flow. The primary function of gate valves is to isolate media. Its design does not cater to flow control.
Structure:
Globe valves and gate valves differ significantly in terms of structure. Globe valves tend to have a complicated structure with most of their components housed internally. Their design allows for a change in flow direction and obstruction, which promotes its throttling function. On the other hand, gate valves have a more simplistic structure. Their components are found on the upper part of the valve body, so they become hollow when the valve is open. Gate valves also have a non-rising or rising stem.
Sealing surfaces:
Globe valves provide a superior seal to gate valves due to its internal valve core, which effectively seals globe valves. Gate valves only seal on the surface of the valve disc, creating a weaker seal.
Application:
Because globe valves experience such drastic pressure changes, they are ideal for application that are unaffected by pressure drops. Gate valves are multidirectional, and they are suitable for applications that are more sensitive to drops in pressure.
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With over 50 years serving the commercial, industrial, HVAC, and plumbing industries, we have the expertise to help you find the right solution for your business. To learn more about our selection of globe and gate valves, contact us or request a quote today.
A Complete Guide To What is Globe Valve
Globe valves have become a necessary instrument in controlling fluid flow. They are used for two major functions as they also operate as on-off valves. These valves have a wide range of applications in several industries, such as water systems, turbine seals, and fuel oil systems.
However, the design of the Globe Valve results in resistance to fluid flow, and this leads to high-pressure drops in the fluid. Therefore, before selecting a globe valve, factors such as pressure drop at positions within the valve and valve sizing should be considered.
This post discusses the function of the globe valve, its parts, installation and maintenance requirements, and other factors to be considered before buying an industrial globe valve.
What Is A Globe Valve?
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Globe valves are valves whose disc or plug moves in a straight line to allow, restrict or regulate the media flow. The vertical movement of the globe valve disc is called linear motion, which is why globe valves are called linear motion valves.
As the disc moves linearly down the valve, the globe valve seat opens to accommodate the discs. The globe valves are primarily used, because of their design, for throttling and regulation of flow through the valve. Still, they can also be used in the on/off services of totally allowing or restricting media.
During passage through the globe valve, the fluid moves up on the side of the seat and against the valve disc before continuing its flow; this cleans the disc and reduces dirt in the valve body.
However, the fluid flow rate and direction are altered and therefore result in a substantial pressure drop as the fluid moves.
Globe Valve Symbol
Source: HardHat Engineering
The globe valve symbol is composed of two triangles meeting at a point. A solid circle is inserted at the meeting point of the triangles, and solid horizontal lines extend from the opposite sides of the triangle.
The horizontal lines show that the globe valve is a two-way inline valve used for throttling and on-off applications.
The globe valve symbol used in piping and instrumentation diagrams (P&ID) is a modification of the valve symbol, which is the same symbol without the solid circle at the meeting point of the two triangles.
The three isometric symbols in the diagram indicate symbols for butt-welding end connections, flanged ends, and socket ends connections.
Types of Globe Valves
Globe valves are of various types and can be differentiated based on their valve body design and body-bonnet connection.
Based On Valve Body Design
Globe valves can be differentiated into three types based on their body design: Angle pattern globe valve, Standard or T-pattern globe valve, and Oblique or Y-pattern globe valve.
Standard Pattern (T-Pattern) Globe Valve
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This valve is a commonly used industrial globe valve. The valve seat is set horizontally so that the disc moves perpendicular to the flow through the pipe flanges.
The standard pattern globe valve obstructs flow in several places in the valve body, leading to a high-pressure drop during the fluid passage. This pattern offers the highest obstruction to flow among the three patterns, and it also has the lowest flow coefficient.
The T-pattern globe valve is used in extreme throttling cases. For example, they are used in processing plant operations in bypass lines required around control valves. Also, they are used in flow regulation operations where pressure losses in the fluid are not important.
Angle Pattern Globe Valve
This pattern is a modified version of the T-pattern. The angle pattern globe valve has its ends at a right angle, and fluid flows after a 90-degree rotation. Angle pattern globe valves have a higher flow coefficient than the standard pattern globe valves.
Because of the ability of the globe valves to handle slug flow of fluid, it is used commonly with fluids of periodic variations and pressure changes. The angle pattern globe valve offers lower obstruction to fluid flow than the standard valves.
Also, when installed near pipeline ends, they decrease the number of pipe joints required and function as a pipe elbow in changing the direction of the fluid flow.
Oblique Pattern (Y-pattern) Globe Valves
The oblique pattern globe valve, out of the three globe valves, offers the least obstruction to fluid flow. Because it least obstructs flow, this results in a decreased fluid pressure drop.
The valve seat is positioned at 45 degrees to the stem, contributing to the direct fluid flow through the valve and the reduction in fluid pressure drop.
The Y-pattern globe valves are not easily susceptible to erosion, even after long periods of fluid flow. During early operation periods, the oblique globe valve is used for flow regulation. Their ability to be cleaned off of sludges when operating in closed lines gives them an advantage over some other valves.
Based On Body-Bonnet Connection
Bonnets are components of the globe and gate valve placed on top of the valve body. The bonnet connects the valve body to the manual lever device or the actuators and grants entry into the valve trim components.
Industrial valve manufacturers uncouple the bonnet from the body for repair and maintenance of globe valves. The body-bonnet connection is important for easy maintenance, checking the seal’s integrity, valve size selection, etc.
Below are the types of globe valves based on the bonnet connection to the valve body :
Bolted Bonnet Connection
Source: Dombor
The bolted bonnet globe valve is also called the screwed-in globe valve. It is the most common and economical connection. The bonnet should not be uncoupled from the valve body often as it may damage the joining areas of the bolts.
The bonnet joints of these valves require large torque in screwing into the valve body and are usually used on valve sizes that are not large.
Welded Bonnet Connection
The welded bonnet globe valve is created by welding the bonnet to the valve body. The bonnet is usually welded completely to the valve body when made of a weldable material.
The welded bonnet connection can be applied to most valve sizes and is functional in different operating conditions.
However, a major disadvantage of the welded bonnet is that uncoupling the connection could damage the bonnet and valve body. Hence, this bonnet connection is used in cases where the valve body can be discarded.
Source: India Mart
Flanged Bonnet Connection
Flanged bonnet globe valves have bolts spread over the connection area. The extra bolts help hold the connection tighter and are more evenly spread than in the bolted connection globe valves. It also allows the flanged bonnet connection to be applied to various sizes of valves and demanding operating conditions.
However, for larger valve sizes, the flanged connection may be welded for safer operations.
Source: India Mart
Union Ring Bonnet Connection
In the union ring bonnet globe valve, the bonnet is joined to the valve body with a union ring. The contact areas for the joints in this bonnet connection are not affected by frequent unscrewing. However, it is used in valve sizes that are not large.
Source: India Mart
Pressure Seal Bonnet Connection
This bonnet connection is most suitable for high temperature and pressure conditions. The pressure seal bonnet globe valve uses fluid pressure to tighten the joint between the bonnet and valve body.
Source: Exporters India
Globe Valve Advantages and Disadvantages
Globe valves are usually compared to the gate and ball valves. While the gate and ball valves function as on-off valves, the globe valve functions as a throttling device in on-off operations. Here are some of its other advantages in piping operations:
Advantages
Good Throttling Ability
The vertical movement of the valve disc to the valve seat encourages the good throttling ability of the globe valve. As the valve is closed, the space between the disc and seat reduces gradually over a short distance, contributing to good flow regulation.
Maintenance and Structure
The globe valve has a simpler construction than the gate valve. With one sealing surface and minimal sealing area, the globe valve reduces construction costs and saves production material.
Maintenance of the globe valve is easy, and it offers a better production process because the valve saves cost and material.
Good Sealing Performance
There is little or no sliding between the valve seat and disc surfaces, leading to less friction between the two surfaces. Therefore, the sealing surfaces experience less wear over a long period and provide good sealing operations.
Also, because the valve seat and disc do not wear easily, the service life of the globe valve is longer than some valves.
Other advantages of the globe valve include:
The installation of globe valves does not require much height as the valves have a thick structure.
Globe valves offer different patterns and types for a wider selection of suitable valves.
Globe valves have fewer seat leakages than when compared to the gate valve.
Disadvantages
These are some disadvantages experienced while using the globe valve:
Large Torque Requirements
The fluid pressure is overcome by the valve disc from the opposite end, requiring large torque to close this valve. Also, to lift the globe valve disc and open the valve, large torque is required.
High Flow Resistance And Pressure Losses
Shutoff valves offer the highest resistance to flow. This resistance occurs because there are various obstructions to fluid flow in the valve. The high resistance also leads to high-pressure losses in the fluid.
Restricted Flow Direction (Unidirectional)
Globe valves restrict the movement of flow to one direction. Fluids can only move from the bottom up or down without changing direction.
Other disadvantages of globe valves include:
They are difficult to install.
They require large openings for the arrangement of discs.
They are power-consuming and noisy.
Globe Valve Functions
Globe Valves function in on-off operations as blocking or isolation valves and in throttling operations to regulate flow. They are largely designed to operate as flow regulators but are also functional when fully open or closed to restrict fluid flow.
As a result of the small height of the globe valve compared to the gate valve, the globe valve disc moves a short distance to the valve seat when opening or closing. The ability of the valve to decrease the space between the valve seat and disc gradually makes it suitable for throttling operations.
Also, globe valves are less likely to be damaged by fluid flow when in a partially open position; this contributes to its effectiveness as a throttling device.
When used in on-off operations, the globe valve disc design is carefully selected to ensure sealing reliability. Linear motion valves such as gate, needle, and globe valves can be applied in many operations with suitable conditions.
Globe Valve Parts
Source: Mechanical Boost
The parts of the globe valve include the actuator, stem, disc (plug), valve body, seat, and bonnet.
Globe Valve Disc
The valve disc is the main part of the globe valve responsible for allowing, restricting, or controlling fluid flow within the pipeline. The valve disc pulls up or moves down in reaction to the stem rotation.
Globe valve discs are designed in three ways: Plug disc design, Composition disc design, and Ball disc design.
Source: Mechanical Boost
Plug Disc Design
These discs have an end that narrows to a flat surface. They are better for use in flow regulation than the ball and composition disc.
Composition Disc Design
Composition discs are suited for water systems because they are hardly eroded. They have a wider surface than the plug and ball disc and are replaceable.
Ball Disc Design
This design is mostly used for on-off operations. It has a narrowing lower end and is usually used in low pressure and temperature conditions.
Globe Valve Seat
The valve seat is the sealing surface for the disc. It is made to accommodate the valve disc as it drops down to close the valve. The globe valve seat can be made with the valve body or screwed. The valve disc connects with the seat at a right angle, resulting in a more reliable seal.
A globe valve back seat is the sealing point for the stem and bonnet above the disc. It holds the media pressure from reaching the valve packing as the valve disc rests on it when fully open.
Globe Valve Stem
The stem connects the disc with the valve actuator. It is usually joined to the bonnet, and the disc can be connected to the stem in two ways: slipping over the stem or screwing into it.
For faster action, the globe valve stem is designed to allow the disc to move in the direction of the fluid as it closes.
Globe Valve Body
This part of the globe valve protects the internal components of the machine. The globe valve is designed to have a simple but solid body construction.
Globe Valve Actuator
The valve actuator rotates the stem, which controls the movement of the valve disc. The opening and closing of the valve are determined first by the actuator. The globe valve actuator is classified into two types based on the requirements of the valves. The types are:
Manually Operated Actuators: These involve using hand wheels or cranks to control the stem.
Automatically Operated Actuators: These involve using electric, pneumatic or hydraulic systems to control the stem.
Globe Valve Bonnet
Bonnets are components of the globe valve placed on top of the valve body. The threaded stem passes through the bonnet through a hole, and the bonnet connects the valve body to the manual lever device or the actuators.
How Does The Globe Valve Work?
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The function of the globe valve is to allow, restrict, or control the flow of media through the pipe from one area to another. To accomplish this, the globe valve uses a valve disc and a valve seat.
The globe valve seat is positioned parallel to and at the center of the pipe. When the handwheel is turned or the actuator is operated automatically, the valve stem is rotated, and the valve disc moves.
For on-off operations, the globe valve disc, controlled by the stem, is either lowered fully to seal with the valve seat and hence block the flow of media or raised fully to allow the flow of media. When the valve disc is raised fully, the fluid flow is at its highest rate, and when it is lowered fully, fluid flow is shut off completely.
For throttling operations, the disc is not fully raised, and the fluid flow occurs in direct proportion to the lifting of the valve disc.
Installation and Maintenance Of Globe Valves
Installation
Proper installation of globe valves decreases premature wear and tear and ensures proper operation of the valves. Upright installation of the globe valves and waste removal inside the valve are some proper installation practices. Some others are:
The internal areas of the valve should be cleaned of fluids before installation.
The valve load should be supported as pipe clampings on the valve may damage it.
Enough space should be provided for the installation of the valve.
When working with flanged connections or bolts, the bolts should be tightened diagonally.
Check the bolts by increasing the pressure inside the valve. Valve pressure is also increased to confirm the reliability of the seal.
The materials of the globe valve components should be checked to ensure no damage was done during transportation or storage of the components.
The pressure rating of the valve should conform to the requirements.
The parts of the pipe flanges to contact the valves should be clean and free of residue.
Maintenance
Maintenance of globe valves increases their service life and ensures they work at optimal conditions. Here are some maintenance practices that enable globe valves to last longer:
The valve should be inspected regularly to ensure leakages are quickly noticed and repaired.
The valve should be cycled regularly when not in use.
If the packing needs to be adjusted, the gland bolts should be carefully tightened as over-tightening may damage the glands. (the gland keeps the packing in a stuffing box)
What To Consider Before Buying Globe Valves
Globe valves are selected based on their suitability to conditions such as temperature, pressure, type of fluid, etc. Therefore selecting the suitable globe valve is based on the valve size, material type, pressure rating, standard, and design of the valve, to select the appropriate globe valve.
Material
Various materials such as cast iron, steel, and plastics, are used in producing globe valves because of their application in most industries. Selecting an appropriate globe valve requires knowledge of the qualities of the media passing through the valve.
Globe valves made with stainless steel are usually used for high-temperature conditions as it is resistant to seizing and galling. Manufacturers should be consulted to know the specific globe valve for different conditions.
Design
Globe valve designs are classified into two types: Valve Body Design and Disc Design. The globe valve body design includes the standard pattern, angle pattern, and oblique pattern.
The standard pattern valve offers the most obstruction to flow, leading to a higher fluid pressure drop in this valve, while the angle pattern valve is suitable for fluids with slug flow. The oblique pattern valves are hardly susceptible to erosion. (These patterns have been explained in detail under globe valve body types)
The globe valve disc design includes the composition disc, plug disc, and ball disc. The composition disc is best suited for water system operations, while the plug discs have the best flow regulation of the three designs. The ball disc is appropriate for low temperature and pressure conditions. (These, too, have already been discussed above under globe valve parts)
Valve Sizes
Valve sizing is essential for throttling valves as the sizes determine how fluid flows through the valve. Selecting the globe valve size requires research and knowledge of the requirements. Usually, the manufacturer sizes the valve for a buyer. Sizing a globe valve is different for each of its functions.
As a throttle valve, the globe valve size is important for calculating the pressure drop at specific positions in the valve.
While functioning in on-off operations, the pressure drop is not monitored as the globe valve functions to allow or restrict fluid. However, a smaller valve size may restrict the flow, but it is a more economical option than the larger valve sizes.
Standards
Below are some important standards used in petrochemical industries for the globe valve:
BS 1873: cast steel valves
API 603: stainless steel valves
API 602/BS 5352: forged steel valves
API 598 and BS EN 12266-1: valves testing
ASME B16.10: face to face dimensions for valves
ASME B16.5 and ASME B16.47: flanged connections
ASME B16.25: butt weld connections design
Conclusion
This post discussed the function of the globe valve, its parts, installation and maintenance requirements, and factors to be considered before buying an industrial globe valve.
Dombor valve is an industrial valve manufacturer that provides high-quality valve solutions to fit market requirements and pipe specifications. We pride ourselves on creating suitable valve types in various conditions. So contact us today!
All About Globe Valves
Guides
Image credit: Tawansak/Shutterstock.com
Globe valves are mainly used to regulate and to stop fluid flow through pipes. They differ from valves such as ball valves and gate valves in that they are specifically designed to govern fluid flow and are not limited to shut-off service. Globe valves are so named because older designs exhibited something of a globular body and could be divided into two hemispheres separated by an equator, where the flow changes direction. The actual internal element that closes against the seat is not usually spherical (as in a ball valve) but more typically flat, semi-spherical, or plug shaped. Globe valves, when opened, are more restrictive to fluid flow than gate or ball valves, resulting in higher pressure drops through them. Globe valves are available in three main body configurations, some of which are intended to reduce the pressure drop through the valve. For information on other valves, please see our Valves Buyers Guide.
Valve design
Globe valves consist of three major portions, the valve body and seat, the disc and stem, and the packing and bonnet. In operation, rotation of the threaded stem through a handwheel or a valve actuator lifts the disc off the seat. Fluid passage through the valve traces a Z-shaped path, enabling the fluid to meet the disc head on. This differs from a gate valve where the fluid passes perpendicularly to the gate. This configuration is sometimes described as a Z-body or Tee pattern valve. Inlets and outlets are situated in line with one another.
Other configurations include Angle and Wye patterns. In the angle globe valve, the outlet is oriented 90° from the inlet and fluid flows along an L-shaped path. In the wye pattern, or Y-body, configuration, the stem enters the valve body at 45°, while inlet and outlet remain in line, as with the tee pattern. The angle pattern is less resistive to flow than the tee pattern, and the wye, less so still. The tee pattern valve is the most common of the three types.
The seal disc is usually made conical to fit the seat but flat-faced discs are used as well. When the valve is opened slightly, fluid flows evenly around the disc and wear on seat and disc is distributed. Thus, the valve works effectively with reduced flow. Ordinarily, flow direction is toward the stem side of the valve but in high-temperature service (steam) the flow is often reversed to keep the disc tightly sealed as the valve body cools and contracts. The valve may orient the flow to use the pressure to aid in closing it (flow over disc) or opening it (flow under disc), and thereby allow the valve to fail closed or fail open.
Seal discs or plugs are usually guided down to the seat through a cage to ensure they make proper contact, especially in higher pressure applications. Some designs employ back seats against which seals on the stem side of the disc press to relieve pressure on the packing when the valve is fully open.
Depending on the design of the sealing element, globe valves may open quickly with a few turns of the stem to rapidly initiate flow (or closed to stop it) or they may open gradually with many stem revolutions to produce more regulated flow through the valve. Although a plug is sometimes used as the sealing element, these should not be confused with plug valves which are quarter-turn devices, similar to ball valves, which use plugs instead of balls to stop and start flow.
Applications
Globe valves are used in wastewater plants, power plants, and process plants for shut-off and regulation service. They are used in steam lines, coolant loops, lubrication systems, etc. where control over the amount of fluid passing through the valve plays a role.
Material selection for globe valve bodies is typically a choice of cast iron or brass/bronze in low-pressure applications and forged carbon steel or stainless steel for higher pressures and temperatures. Specifying material for the body generally includes all components under pressure, while “trim” refers to the components apart from the body, including the seats, the disc, and the stem. Larger sizes are identified by an ASME class pressure rating and ordered with standard bolted or welded flanges. Sizing a globe valve takes more effort than sizing some other valve types as pressure drop through the valve may be a concern.
Rising stem designs are most common among globe valves but non-rising stem valves may be found. Bonnets are usually bolt-on designs which can be removed readily for internal inspection of the valve. Seats and discs are easily replaced.
Globe valves are routinely automated using pneumatic piston or diaphragm actuators which act directly on the stem to move the valve disc into position. The piston/diaphragm can be spring biased to open or close the valve under loss of air pressure. Electric rotary actuators are used as well.
Some building codes require on/off valves be installed upstream of certain equipment, on water heater inlets, for example. Here, a ball or gate valve is acceptable while a globe valve is not.
Considerations
Globe valves are primarily control valves and are excellent candidates for automation. Many manufacturers offer integral valve and actuator assemblies for this use. In some cases, the valve will be fitted with a direct-acting stem that actuates through a piston or diaphragm, precluding the use of a traditional threaded stem. These valves usually include a manual override for operating the valve by hand. Since sizing a valve actuator is an exercise in itself, these integrated valve-actuator combinations can take some of the labor out of specifying an automated system.
Summary
This article presented a review of globe valves, including their design, applications, and selection considerations. For more information on related products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products. More information on valves in general can be found at the Valve Manufacturers Association website, www.vma.org.
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