May. 20, 2024
Mechanical Parts & Fabrication Services
Courtesy: CFE Media and Technology
Manufacturing and processing facilities often work with systems that manage fluids in their operations. These facilities must control the supply and flow of different service fluids crucial for routine processes. The service fluids can be gaseous, liquid or semi-solid (slurries), bearing unique physical and chemical properties.
Any system with a working fluid will need valves to control fluid flow, while also being able to handle operating characteristics like temperature and pressure. Valves come into play in these situations, by performing the functions needed to manage the working fluid.
With the many different types of valves and even more choices for customization, choosing a valve can seem like a daunting task. Regardless of the nature of the application, impacts on safety and effectiveness are always a top priority. Here are some practical factors to start with when choosing an appropriate valve.
Not all fluid systems are pressurized to the same level. Different types of service will require higher pressure levels than others. However, the entire system should be able to deal with the demands of the conditions, and within a reasonable factor of safety. Line pressure refers specifically to the force exerted throughout the area of the valve body. It provides a figure for the full upstream pressure of the fluid as it enters the valve.
Going beyond design pressure limits means running the risk of ineffective valve operations. Leaking fluids is a common consequence of exceeding pressure limits, causing line losses and safety concerns. Any additional stress beyond the design parameters of a valve can also compromise sealing components and can lead to the valve degrading.
When selecting valves based on the line pressure of the piping system, process engineers should evaluate the desired pressure drop across the valve and the entire piping system. The valve trim and sizing should offer the least frictional resistance to keep the pressure drop across the valve low and reduce line pressure losses — which may affect subsequent manufacturing processes. This explains why gate valves, which have low-pressure drops at fully open positions, are preferable to globe valves in industrial piping systems where line pressure should remain constant.
Certain valves require additional considerations such as the set pressure for safety relief valves (SRV). Aside from evaluating the maximum pressure expected from the line, the design needs to account for the pressure level at which the valve opens a path to relieve system pressure. A similar concept applies to check valves, where cracking pressure is the minimum pressure where it starts to allow flow in one direction.
Different valve types and their varying mechanisms manage fluid flow in distinctive ways. For instance, a ball valve offers superb sealing for shut-off applications. However, a needle valve might provide better precision for controlling specific flow rates. The valve’s inner workings tell a lot about how they steer the working fluid and how they perform the required function.
Valve selection requires understanding what the flow needs to be. Broad classifications of valve functions include whether the valve needs to switch the flow on or off, regulate the amount of flow or change the flow’s direction.
On-off applications require the valve to either allow or restrict flow. The way a ball valve works is an excellent example of a rapid response, where a hollowed-out spherical ball either aligns with or blocks fluid flow. A gate valve provides the same function — shutting off flow — using a plate or obstructive tool that acts as a gate. Butterfly valves can also provide on-off fluid service using a metal disc (butterfly) that completes quarter-turn rotations around a fixed axis to permit or stop the flow of service fluids.
Flow control functions need more precise increments in adjusting the flow rate. Rather than shutting and opening the flow passage, the valve should be able to handle more meticulous control. Controlling flow rates is only possible if the action of opening the valve has a predictable relationship with the variation of flow allowed through the valve. Needle valves achieve this level of precision by employing a needle-shaped plunger — often coupled with a screw-type controller — that restricts flow. One can achieve linear flow control using V-ball valves whose flow rates increase with shaft rotations. V-ball valves have low pressure drops, provide bubble-tight shut-off, and are designed for high pressure and flow service.
Process engineers can achieve precise flow control using sliding gate valves that feature a compact design and require low actuation forces. Sliding gate valves are lightweight and compact, which make them more responsive to line pressure changes. Plug valves also are suitable alternatives when considering precise flow control in different industrial piping systems.
Think of controlling directional flow as an expansion of the concept of on/off applications. It can refer to either the limitation of flow direction or the management of multiple possible inlets and outlets. Check valves are an example of limiting fluid flow to go one way.
A minimum set pressure will allow flow rates to go in one direction but not the other.
Another example of directional control is a situation in which the flow is not shut in one path but redirected onto another. Multi-port valves that allow on-off functionality, such as a 3-way ball valve, are available in configurations that permit multiple exit ports or inlets.
As with pressure, temperature affects the characteristics of both the medium flowing through the line and the valve itself. Working fluids can have varying energy levels dependent on temperature levels. Extreme temperature conditions can also exacerbate the corrosive effects of fluids on certain materials. Several materials also make up individual valve components and these materials withstand high and low temperatures differently.
Fluids, especially gases, often take up more space as the temperature rises. Gases expand and contract with varying temperatures. Air and other gases that experience high temperatures tend to be less dense — resulting in increased pressure rating requirements if the fluid is enclosed, or higher flow rates if allowed to pass through. Valve considerations need to account for higher pressure ratings or more precise increments for flow control in these situations.
Aside from affecting the fluid that goes through the system, temperature ratings also affect the valve and its components. Materials often contract at low temperatures and expand with higher temperatures. Because many different materials make up a valve, temperature differences can result in non-uniform changes in the components of a valve.
Metals and metal alloys are the most common materials used for the valve body. Various stainless steel variants are a sensible start for non-corrosive gases up to around 400 °F. Austenitic steels and nickel alloys are typical alternatives for higher temperatures that are also viable for corrosive service. On the other hand, Teflon is considered a versatile seat material that works for both ends of the temperature spectrum — as opposed to EPDM rubber, which offers a narrower range of temperature allowances. Always consult a valve expert when designing or sizing valves for critical fluid service to avoid valve problems or failures during use.
Typical temperature ranges for valve types also apply. All industrial valves are assigned temperature classes depending on the manufacturing materials and testing standards. Categorizing valves based on allowable temperature range makes it easier to select the correct process valves and ensure durable service. High-temperature process valves use strong manufacturing materials (including alloys) to prevent chemical reactions with different service fluids, or deformations when controlling fluid flow at high process temperatures. Exercise caution when selecting valves for low-temperature (cryogenic) applications.
Selecting a valve comes with budget constraints. Different types of valves have varying levels of associated construction costs. The type of valve material and the anticipated medium affect any special requirements for the valve construction material and the budget. Customizations regarding valve operation and automation also incur additional costs. Utilizing actuators requires more specialized components, which translates to added expenses.
Looking specifically at valve construction, simpler valves with fewer moving parts often cost less for the same rating. For instance, a gate valve typically costs less than a ball valve for similar specifications due to its design. However, the very design that makes gate valves cheaper in construction also makes them less effective when it comes to sealing.
Choosing to operate a valve manually or automatically is another consideration that affects total cost. Selecting an actuator that allows remote and automated control can sustain additional expenses. Actuators typically employ hydraulic, pneumatic or electrical means of operation. Choose a valve within the company’s budget and can provide dependable and durable fluid control. The goal is to minimize the total cost of valve ownership — purchasing and maintaining valves throughout their useful lives — irrespective of their valve cycles and sizes.
Hydraulic actuators use compressed oil, which allows quick-response operations for large-scale valves due high-force capacities. Additional safety precautions also should be in place when handling hydraulic fluid because maintenance practices can be complex.
Pneumatic actuators use air instead of oil, making them more suitable for hazardous applications. However, there will be drawbacks in reduced precision due to the compressibility of air. It is crucial to maintain accessibility to instrument-quality air. The presence of impurities in compressed air can accelerate the wear and tear of actuators and adjacent valve components. With smaller-scale operations, electrical actuators are relatively inexpensive alternatives. They are also generally more compact and lighter if slower actuation speeds are acceptable.
Budget and effectiveness become a balancing act depending on the requirements of an application. While there are opportunities to get cheaper alternatives, the impact on achieving business objectives and workplace safety remains the priority.
Valve selection is not a choice guided by preference. Instead, most considerations arise from utility and the necessity of meeting the specifications of the operating conditions.
Ball valves are designed for industrial fluid applications and a good starting point when selecting a valve. They offer reliable sealing that lends itself to on-off applications. Because the hollowed-out portion of the ball allows unobstructed flow when switched on, it achieves minimal pressure reduction across the valve. While most ball valve types are suitable for moderate to high pressures, large ball valve applications can use a trunnion-mounted ball valve to offer additional mechanical support for stability.
Gate valves are a suitable alternative for the same on-off applications if the user prefers a more gradual flow release. This preference is more applicable to water systems where the effect of water hammer requires additional consideration. For any other application, gate valves also have the advantage of generally costing less than other alternatives.
For functions requiring flow control, needle valves offer high levels of precision. Typical applications include gas calibration and lines carrying clear fluids such as propane. A more economical option for industrial, high-flow functions are globe valves.
Globe valves utilize a disc element that linearly adjusts its position to obstruct or permit flow. This element is usually coupled with a screw-type control that allows for gradual flow rate increments. Increasing or decreasing the amount of the opening proportionally affects the amount of flow, which then allows control. Different configurations of globe valves also enable varying flow patterns such as crossflow and Y-flow arrangements.
Butterfly valves are another option for industrial piping systems. They have a compact and lightweight design, rendering them more responsive to pressure changes in the pipeline with excellent sealing characteristics. Several butterfly valve designs are available to meet industrial fluid system pressure and temperature demands.
Regardless of the type of valve used for various applications, design considerations should also include assessing suitable valve materials. The toxicity of fluids and any corrosive properties mandate using materials that can chemically handle the wear. Exceedingly hot or cold conditions also require proper material type.
While there’s a broad range of valve options, the good news is facilities can count on having a valve that will perform the duties they require. Regardless of what type of valve design one ends up with, it is always a top priority to keep operations safe and effective. Always work with a valve expert when selecting valves for different fluid applications to ensure proper sizing and maximize the productivity and efficiency of industrial processes.
ValveMan is a CFE Media and Technology content partner.
Do you have experience and expertise with the topics mentioned in this content? You should consider contributing to our CFE Media editorial team and getting the recognition you and your company deserve. Click here to start this process.
The gate valve is the most common shut-off valve. Unlike ball valves, they are not quarter-turn devices; instead, they close and open through revolutions of the hand wheel.
Used in wastewater plants, power plants and process systems, the threaded system of the gate valves give them an advantage over the quarter turn system of the ball and butterfly valve in large applications.
Fluid through gate valves experiences only minimal pressure drop as gate valves allow total flow through its passage when fully open.
This post discusses the functions, symbols, advantages and disadvantages, types, and other essential things you need to know about the gate valve.
Gate valves can also be called sluice valves or knife valves. They are control valves that allow or restrict the flow of media completely. Gate valves use a flat gate to close off flow between pipe flanges.
A gate valve, being a full port valve, has an equal diameter to the pipe through which the fluid passes. Hence, unlike butterfly valves, gate valves minimise pressure losses in the fluid when fully open. Also, because of the equal pipe and valve diameters, gate valves allow for the movement of pigs within the pipe for cleaning and inspection operations.
While butterfly valves can be used in flow regulation and on-off services, gate valves should only be used in on-off services as blocking valves and also to allow fluid flow. They should not be used in throttling.
Because of their uncomplicated construction and capability to be used in different low-pressure applications, gate valves are one of the most common valves in the industry.
The gate valve symbol is composed of two triangles meeting at a point. A vertical line is inserted between the triangles, and solid horizontal lines extend from the opposite sides of the triangle.
The vertical line indicates the blocking operation of the gate valve, and the horizontal lines show that the valve has a two-way function in on-off applications.
The gate valve symbol used in piping and instrumentation diagrams (P&ID) is a modification of the valve symbol, which is the gate valve symbol without the vertical line between the triangles.
The three isometric symbols in the diagram indicate symbols for butt-welding end connections, flanged ends, and socket ends connections.
Gate valves can be classified in three different ways:
Gate valves are mostly differentiated into parallel and wedge-shaped valves. The parallel gate valves shut off flow using a flat gate between two parallel seats. The gate is shut when the pressure from the pipe is allowed to seal the disc to prevent any flow. These gate valves usually function in conditions with minimal pressures or pressure drops.
The gate in the metal seated gate valve is shaped like a cone and enters into a hole in the bottom of the valve when it closes, supported by inclined seats. Impurities are a constant feature of the metal seated valve because of its closure design, leading to wearing out of the gate.
Link to BSTV
The metal seated gate valve was used before producing resilient seated gate valves.
Resilient seated gate valves, because of the valve’s flat base, allow impurities to pass through without being stored in a hole as in the metal seated gate valve.
The rubber element in the gate sucks in the impurities as it closes, and the impurities are cleaned off when it opens again, allowing the gate to return to its normal form.
Rising stem-designed gate valves have stems outside the valve body and move with the gate. As the gate moves upward, so does the stem and vice versa. This movement allows the stem to be monitored for maintenance. This design is best used for surface installations.
Source: AlibabaIn non-rising stem designs, the stem rotates with the gate movement from inside the valve body. An indicator on top of the stem shows the position of the valve. This design can be used in industrial gate valves for surface and underground installations.
These valves seal by the combination of two slab gate valves. The mechanically expanding gates are sealed effectively at the gate seats. They find application mostly in electric systems and petroleum industries.
When used as a control valve, the gate valve can effectively function in several industrial operations. Like other industrial control valves, the gate valve has advantages and disadvantages. Some of its advantages are:
The gate valve is a full port valve. Hence it allows easy passage of fluid with minimal resistance. Unlike other valves, when fully open, the gate valve body does not affect the flow motion or direction.
Gate valves perform better sealing operations than the shutoff valve, which is also a control valve. Even though slower than some other valves, the gate valve offers faster opening and closing operations than the shutoff valve.
Gate valves can function effectively with fluids such as oil, steam, slurries, and suspended fluids. Also, they can function as low vacuum system valves or venting valves.
Gate valves are not restricted to one direction of flow. They are two-way directional valves, and they do not depend on the direction of the medium. Gate valves are good for operations where the fluid direction may switch.
Other advantages of the gate valves include:
Gate valves can be severely damaged if they are open or closed halfway. Hence the gate has to be withdrawn fully into the upper valve area when open and must be allowed to rest on the valve seat when closed before fluid flow.
The movement from the upper valve area to the bottom takes a lot of time, leading to the slow operation of gate valves. Due to its slow operation, gate valves can not be used for fast processes.
The valve gate makes contact frequently with the valve seat; this may lead to scrapings on the gate surface. Surface scrapings cause damage to the gate with time resulting in the shorter life span of gate valves. Damages on the gate surface are not easily repaired.
Other disadvantages of gate valves include:
Gate valves are usually used in on/off services where they function in allowing or restricting flow. For better efficiency, gate valves should not be used regularly, as frequent friction would lead to the shorter service life of the valve.
Because of its ability to allow flow through the pipeline with minimal pressure losses and permit easy operation of pigs for inspection and cleaning, the gate valve is a commonly used valve for blocking and isolation.
However, gate valves should not be used for flow regulation. Constant fluid contact with the gate causes damage to the disc and seat and invariably shortens the valve’s service life.
They have a wide application in the industry which includes operations in petroleum refineries, power plants, manufacturing factories, and chemical production companies. The gate valves function effectively in high temperature and pressure conditions.
The gate valve includes the body, hand wheel, yoke, bonnet, packing gland, stew, and gate. Each part will be explained below.
The valve body is responsible for housing the valve trim and allowing fluid to pass from one pipe end to another. Valve bodies are made from metals, an alloy of metals, or nonmetals of varying kinds.
Also called shells, the gate valve body can be joined to the pipe flanges by butt, sockets, wafers, or threaded ends.
The gate valve body is of three different designs, which depend on the purpose of the gate valve. The designs are Reduced Bore, Full Bore, and Cross Flow.
The bonnet of gate valves primarily functions as valve covers and support for other parts of the valve, such as the disc, stem, and actuators. Also, in the gate valve, the bonnet allows an opening for the stem.
The gate valve bonnet is joined to the body using threads, bolts, or welding. Some valve bonnets are designed to be merged with the body (bonnetless valves), and bonnets are usually made in the same material as the valve body.
The gate valve trim comprises the valve disc, gland sleeve, gland packings, back seat, valve stem, and valve seat. These are parts that have contact with the flow medium. The valve trim parts control the operation of the valve.
The stem is responsible for the control of the disc. When the stem is rotated, it relays this motion to the disc by lifting or dropping it. The gate valve stem is joined to the actuator (sometimes through the yoke) or manual handling machine on the top end and the valve disc on the other end to facilitate control.
The gate valve seat is a resting point for the valve disc to which it is sealed. While some valves have one seat, the gate valve has two seats, one on each end of the pipe flanges. If the disc and valve seat are not sealed properly, it may cause leakages in the valve.
The gate valve backseat holds the stem in the valve open position. It also restricts fluid from going up to the packing chamber and the surface.
The gate valve disc is the part of the valve which performs the function of allowing or restricting flow through the pipeline. It blocks the fluid pressure from moving from one end to another. The disc rests on the valve seat to which it is sealed.
The gland packings prevent leakages from the stem and are usually in a stuffing box. The gland sleeves keep the gland packings in the box.
The yoke connects the actuator to the stem. They are sometimes merged with the bonnet to manufacture several valve designs. The yoke is also called arms.
The gate valve operation is in many ways similar to the operation of most valves. The hand wheel or actuator is controlled to rotate the stem, which controls the gate. For the handwheel, the wheel is turned in several revolutions before the gate valve can be fully open from a closed position or fully closed from an open position.
Control using the actuator is easier as it requires no user at the location, only an actuator system (pneumatic or electric) must be on site. By raising the gate to a fully open position, the valve allows the media to flow through the pipeline without obstruction.
Closing and sealing the pipe to the valve seat retains the flow pressure and restricts the flow of the media beyond the gate. The flow rate of the media experiences erratic change as the gate valve is closed, resulting in an unpredictable relationship between the valve and fluid flow rate.
Fluid pressure and flow against the gate wear out the seat and gate. Gate valves should not be used for flow regulation as the constant flow hastens the damage to the gate and seat.
Installing gate valves should be done properly to increase the service life of the gate valves and to ensure their proper operation. Here are some installation practices to be followed while installing gate valves:
Below are some essential practices to ensure the valve works effectively and lasts longer.
In selecting a gate valve suitable for operation in specific conditions, factors such as suitable material, size and design must be considered. Here are some factors to consider in buying a gate valve:
Materials used for the production of gate valves vary with specific conditions. Common materials are cast iron, cast carbon steel, stainless steel, ductile iron, gun metal, bronze, steel alloys, stainless steel, and forged steel.
Key selection criteria of material to use are fluid service and design temperature. Below are some materials used in the creation of the gate valve:
Material Grades
Below are some common trim material grades used in the production of gate valves
Trim materials are grouped and assigned a trim number or combination number. In the chart below, material for a gate valve seat, disc, stem and backseat are specified against a trim number.
From this chart, an order can be made by the trim number. There will be no need to specify any materials for an order of the gate valve trim. This chart is in line with the API 600 specification.
Source: HardHat EngineeringBelow are codes and standards that are used in the design and selection of gate valves:
API 598
API B16.34
ANSI B16.10
ANSI B16.25 and B16.11
ANSI B 1.20.1 (BSP/NPT)
This post discussed all you need to know about the gate valve, including its function, parts, installation and maintenance requirements, and what you need to consider before buying an industrial gate valve.
Dombor valve is an industrial valve manufacturer that provides high-quality valve solutions to fit market requirements. With our 20 years of manufacturing experience, we specialise in creating valve types that function in any environment. You can contact us today for the best professional gate valves.
Courtesy: CFE Media and Technology
Manufacturing and processing facilities often work with systems that manage fluids in their operations. These facilities must control the supply and flow of different service fluids crucial for routine processes. The service fluids can be gaseous, liquid or semi-solid (slurries), bearing unique physical and chemical properties.
Any system with a working fluid will need valves to control fluid flow, while also being able to handle operating characteristics like temperature and pressure. Valves come into play in these situations, by performing the functions needed to manage the working fluid.
With the many different types of valves and even more choices for customization, choosing a valve can seem like a daunting task. Regardless of the nature of the application, impacts on safety and effectiveness are always a top priority. Here are some practical factors to start with when choosing an appropriate valve.
Not all fluid systems are pressurized to the same level. Different types of service will require higher pressure levels than others. However, the entire system should be able to deal with the demands of the conditions, and within a reasonable factor of safety. Line pressure refers specifically to the force exerted throughout the area of the valve body. It provides a figure for the full upstream pressure of the fluid as it enters the valve.
Going beyond design pressure limits means running the risk of ineffective valve operations. Leaking fluids is a common consequence of exceeding pressure limits, causing line losses and safety concerns. Any additional stress beyond the design parameters of a valve can also compromise sealing components and can lead to the valve degrading.
When selecting valves based on the line pressure of the piping system, process engineers should evaluate the desired pressure drop across the valve and the entire piping system. The valve trim and sizing should offer the least frictional resistance to keep the pressure drop across the valve low and reduce line pressure losses — which may affect subsequent manufacturing processes. This explains why gate valves, which have low-pressure drops at fully open positions, are preferable to globe valves in industrial piping systems where line pressure should remain constant.
Certain valves require additional considerations such as the set pressure for safety relief valves (SRV). Aside from evaluating the maximum pressure expected from the line, the design needs to account for the pressure level at which the valve opens a path to relieve system pressure. A similar concept applies to check valves, where cracking pressure is the minimum pressure where it starts to allow flow in one direction.
Different valve types and their varying mechanisms manage fluid flow in distinctive ways. For instance, a ball valve offers superb sealing for shut-off applications. However, a needle valve might provide better precision for controlling specific flow rates. The valve’s inner workings tell a lot about how they steer the working fluid and how they perform the required function.
Valve selection requires understanding what the flow needs to be. Broad classifications of valve functions include whether the valve needs to switch the flow on or off, regulate the amount of flow or change the flow’s direction.
On-off applications require the valve to either allow or restrict flow. The way a ball valve works is an excellent example of a rapid response, where a hollowed-out spherical ball either aligns with or blocks fluid flow. A gate valve provides the same function — shutting off flow — using a plate or obstructive tool that acts as a gate. Butterfly valves can also provide on-off fluid service using a metal disc (butterfly) that completes quarter-turn rotations around a fixed axis to permit or stop the flow of service fluids.
Flow control functions need more precise increments in adjusting the flow rate. Rather than shutting and opening the flow passage, the valve should be able to handle more meticulous control. Controlling flow rates is only possible if the action of opening the valve has a predictable relationship with the variation of flow allowed through the valve. Needle valves achieve this level of precision by employing a needle-shaped plunger — often coupled with a screw-type controller — that restricts flow. One can achieve linear flow control using V-ball valves whose flow rates increase with shaft rotations. V-ball valves have low pressure drops, provide bubble-tight shut-off, and are designed for high pressure and flow service.
Process engineers can achieve precise flow control using sliding gate valves that feature a compact design and require low actuation forces. Sliding gate valves are lightweight and compact, which make them more responsive to line pressure changes. Plug valves also are suitable alternatives when considering precise flow control in different industrial piping systems.
Think of controlling directional flow as an expansion of the concept of on/off applications. It can refer to either the limitation of flow direction or the management of multiple possible inlets and outlets. Check valves are an example of limiting fluid flow to go one way.
A minimum set pressure will allow flow rates to go in one direction but not the other.
Another example of directional control is a situation in which the flow is not shut in one path but redirected onto another. Multi-port valves that allow on-off functionality, such as a 3-way ball valve, are available in configurations that permit multiple exit ports or inlets.
As with pressure, temperature affects the characteristics of both the medium flowing through the line and the valve itself. Working fluids can have varying energy levels dependent on temperature levels. Extreme temperature conditions can also exacerbate the corrosive effects of fluids on certain materials. Several materials also make up individual valve components and these materials withstand high and low temperatures differently.
Fluids, especially gases, often take up more space as the temperature rises. Gases expand and contract with varying temperatures. Air and other gases that experience high temperatures tend to be less dense — resulting in increased pressure rating requirements if the fluid is enclosed, or higher flow rates if allowed to pass through. Valve considerations need to account for higher pressure ratings or more precise increments for flow control in these situations.
Aside from affecting the fluid that goes through the system, temperature ratings also affect the valve and its components. Materials often contract at low temperatures and expand with higher temperatures. Because many different materials make up a valve, temperature differences can result in non-uniform changes in the components of a valve.
Metals and metal alloys are the most common materials used for the valve body. Various stainless steel variants are a sensible start for non-corrosive gases up to around 400 °F. Austenitic steels and nickel alloys are typical alternatives for higher temperatures that are also viable for corrosive service. On the other hand, Teflon is considered a versatile seat material that works for both ends of the temperature spectrum — as opposed to EPDM rubber, which offers a narrower range of temperature allowances. Always consult a valve expert when designing or sizing valves for critical fluid service to avoid valve problems or failures during use.
Typical temperature ranges for valve types also apply. All industrial valves are assigned temperature classes depending on the manufacturing materials and testing standards. Categorizing valves based on allowable temperature range makes it easier to select the correct process valves and ensure durable service. High-temperature process valves use strong manufacturing materials (including alloys) to prevent chemical reactions with different service fluids, or deformations when controlling fluid flow at high process temperatures. Exercise caution when selecting valves for low-temperature (cryogenic) applications.
Selecting a valve comes with budget constraints. Different types of valves have varying levels of associated construction costs. The type of valve material and the anticipated medium affect any special requirements for the valve construction material and the budget. Customizations regarding valve operation and automation also incur additional costs. Utilizing actuators requires more specialized components, which translates to added expenses.
Looking specifically at valve construction, simpler valves with fewer moving parts often cost less for the same rating. For instance, a gate valve typically costs less than a ball valve for similar specifications due to its design. However, the very design that makes gate valves cheaper in construction also makes them less effective when it comes to sealing.
Choosing to operate a valve manually or automatically is another consideration that affects total cost. Selecting an actuator that allows remote and automated control can sustain additional expenses. Actuators typically employ hydraulic, pneumatic or electrical means of operation. Choose a valve within the company’s budget and can provide dependable and durable fluid control. The goal is to minimize the total cost of valve ownership — purchasing and maintaining valves throughout their useful lives — irrespective of their valve cycles and sizes.
Hydraulic actuators use compressed oil, which allows quick-response operations for large-scale valves due high-force capacities. Additional safety precautions also should be in place when handling hydraulic fluid because maintenance practices can be complex.
Pneumatic actuators use air instead of oil, making them more suitable for hazardous applications. However, there will be drawbacks in reduced precision due to the compressibility of air. It is crucial to maintain accessibility to instrument-quality air. The presence of impurities in compressed air can accelerate the wear and tear of actuators and adjacent valve components. With smaller-scale operations, electrical actuators are relatively inexpensive alternatives. They are also generally more compact and lighter if slower actuation speeds are acceptable.
Budget and effectiveness become a balancing act depending on the requirements of an application. While there are opportunities to get cheaper alternatives, the impact on achieving business objectives and workplace safety remains the priority.
Valve selection is not a choice guided by preference. Instead, most considerations arise from utility and the necessity of meeting the specifications of the operating conditions.
Ball valves are designed for industrial fluid applications and a good starting point when selecting a valve. They offer reliable sealing that lends itself to on-off applications. Because the hollowed-out portion of the ball allows unobstructed flow when switched on, it achieves minimal pressure reduction across the valve. While most ball valve types are suitable for moderate to high pressures, large ball valve applications can use a trunnion-mounted ball valve to offer additional mechanical support for stability.
Gate valves are a suitable alternative for the same on-off applications if the user prefers a more gradual flow release. This preference is more applicable to water systems where the effect of water hammer requires additional consideration. For any other application, gate valves also have the advantage of generally costing less than other alternatives.
For functions requiring flow control, needle valves offer high levels of precision. Typical applications include gas calibration and lines carrying clear fluids such as propane. A more economical option for industrial, high-flow functions are globe valves.
Globe valves utilize a disc element that linearly adjusts its position to obstruct or permit flow. This element is usually coupled with a screw-type control that allows for gradual flow rate increments. Increasing or decreasing the amount of the opening proportionally affects the amount of flow, which then allows control. Different configurations of globe valves also enable varying flow patterns such as crossflow and Y-flow arrangements.
Butterfly valves are another option for industrial piping systems. They have a compact and lightweight design, rendering them more responsive to pressure changes in the pipeline with excellent sealing characteristics. Several butterfly valve designs are available to meet industrial fluid system pressure and temperature demands.
Regardless of the type of valve used for various applications, design considerations should also include assessing suitable valve materials. The toxicity of fluids and any corrosive properties mandate using materials that can chemically handle the wear. Exceedingly hot or cold conditions also require proper material type.
While there’s a broad range of valve options, the good news is facilities can count on having a valve that will perform the duties they require. Regardless of what type of valve design one ends up with, it is always a top priority to keep operations safe and effective. Always work with a valve expert when selecting valves for different fluid applications to ensure proper sizing and maximize the productivity and efficiency of industrial processes.
ValveMan is a CFE Media and Technology content partner.
Do you have experience and expertise with the topics mentioned in this content? You should consider contributing to our CFE Media editorial team and getting the recognition you and your company deserve. Click here to start this process.
The gate valve is the most common shut-off valve. Unlike ball valves, they are not quarter-turn devices; instead, they close and open through revolutions of the hand wheel.
Used in wastewater plants, power plants and process systems, the threaded system of the gate valves give them an advantage over the quarter turn system of the ball and butterfly valve in large applications.
Fluid through gate valves experiences only minimal pressure drop as gate valves allow total flow through its passage when fully open.
This post discusses the functions, symbols, advantages and disadvantages, types, and other essential things you need to know about the gate valve.
Gate valves can also be called sluice valves or knife valves. They are control valves that allow or restrict the flow of media completely. Gate valves use a flat gate to close off flow between pipe flanges.
A gate valve, being a full port valve, has an equal diameter to the pipe through which the fluid passes. Hence, unlike butterfly valves, gate valves minimise pressure losses in the fluid when fully open. Also, because of the equal pipe and valve diameters, gate valves allow for the movement of pigs within the pipe for cleaning and inspection operations.
While butterfly valves can be used in flow regulation and on-off services, gate valves should only be used in on-off services as blocking valves and also to allow fluid flow. They should not be used in throttling.
Because of their uncomplicated construction and capability to be used in different low-pressure applications, gate valves are one of the most common valves in the industry.
The gate valve symbol is composed of two triangles meeting at a point. A vertical line is inserted between the triangles, and solid horizontal lines extend from the opposite sides of the triangle.
The vertical line indicates the blocking operation of the gate valve, and the horizontal lines show that the valve has a two-way function in on-off applications.
The gate valve symbol used in piping and instrumentation diagrams (P&ID) is a modification of the valve symbol, which is the gate valve symbol without the vertical line between the triangles.
The three isometric symbols in the diagram indicate symbols for butt-welding end connections, flanged ends, and socket ends connections.
Gate valves can be classified in three different ways:
Gate valves are mostly differentiated into parallel and wedge-shaped valves. The parallel gate valves shut off flow using a flat gate between two parallel seats. The gate is shut when the pressure from the pipe is allowed to seal the disc to prevent any flow. These gate valves usually function in conditions with minimal pressures or pressure drops.
The gate in the metal seated gate valve is shaped like a cone and enters into a hole in the bottom of the valve when it closes, supported by inclined seats. Impurities are a constant feature of the metal seated valve because of its closure design, leading to wearing out of the gate.
The metal seated gate valve was used before producing resilient seated gate valves.
Resilient seated gate valves, because of the valve’s flat base, allow impurities to pass through without being stored in a hole as in the metal seated gate valve.
The rubber element in the gate sucks in the impurities as it closes, and the impurities are cleaned off when it opens again, allowing the gate to return to its normal form.
Rising stem-designed gate valves have stems outside the valve body and move with the gate. As the gate moves upward, so does the stem and vice versa. This movement allows the stem to be monitored for maintenance. This design is best used for surface installations.
Source: AlibabaIn non-rising stem designs, the stem rotates with the gate movement from inside the valve body. An indicator on top of the stem shows the position of the valve. This design can be used in industrial gate valves for surface and underground installations.
These valves seal by the combination of two slab gate valves. The mechanically expanding gates are sealed effectively at the gate seats. They find application mostly in electric systems and petroleum industries.
When used as a control valve, the gate valve can effectively function in several industrial operations. Like other industrial control valves, the gate valve has advantages and disadvantages. Some of its advantages are:
The gate valve is a full port valve. Hence it allows easy passage of fluid with minimal resistance. Unlike other valves, when fully open, the gate valve body does not affect the flow motion or direction.
Gate valves perform better sealing operations than the shutoff valve, which is also a control valve. Even though slower than some other valves, the gate valve offers faster opening and closing operations than the shutoff valve.
Gate valves can function effectively with fluids such as oil, steam, slurries, and suspended fluids. Also, they can function as low vacuum system valves or venting valves.
Gate valves are not restricted to one direction of flow. They are two-way directional valves, and they do not depend on the direction of the medium. Gate valves are good for operations where the fluid direction may switch.
Other advantages of the gate valves include:
Gate valves can be severely damaged if they are open or closed halfway. Hence the gate has to be withdrawn fully into the upper valve area when open and must be allowed to rest on the valve seat when closed before fluid flow.
The movement from the upper valve area to the bottom takes a lot of time, leading to the slow operation of gate valves. Due to its slow operation, gate valves can not be used for fast processes.
The valve gate makes contact frequently with the valve seat; this may lead to scrapings on the gate surface. Surface scrapings cause damage to the gate with time resulting in the shorter life span of gate valves. Damages on the gate surface are not easily repaired.
Other disadvantages of gate valves include:
Gate valves are usually used in on/off services where they function in allowing or restricting flow. For better efficiency, gate valves should not be used regularly, as frequent friction would lead to the shorter service life of the valve.
Because of its ability to allow flow through the pipeline with minimal pressure losses and permit easy operation of pigs for inspection and cleaning, the gate valve is a commonly used valve for blocking and isolation.
However, gate valves should not be used for flow regulation. Constant fluid contact with the gate causes damage to the disc and seat and invariably shortens the valve’s service life.
They have a wide application in the industry which includes operations in petroleum refineries, power plants, manufacturing factories, and chemical production companies. The gate valves function effectively in high temperature and pressure conditions.
The gate valve includes the body, hand wheel, yoke, bonnet, packing gland, stew, and gate. Each part will be explained below.
The valve body is responsible for housing the valve trim and allowing fluid to pass from one pipe end to another. Valve bodies are made from metals, an alloy of metals, or nonmetals of varying kinds.
Also called shells, the gate valve body can be joined to the pipe flanges by butt, sockets, wafers, or threaded ends.
The gate valve body is of three different designs, which depend on the purpose of the gate valve. The designs are Reduced Bore, Full Bore, and Cross Flow.
The bonnet of gate valves primarily functions as valve covers and support for other parts of the valve, such as the disc, stem, and actuators. Also, in the gate valve, the bonnet allows an opening for the stem.
The gate valve bonnet is joined to the body using threads, bolts, or welding. Some valve bonnets are designed to be merged with the body (bonnetless valves), and bonnets are usually made in the same material as the valve body.
The gate valve trim comprises the valve disc, gland sleeve, gland packings, back seat, valve stem, and valve seat. These are parts that have contact with the flow medium. The valve trim parts control the operation of the valve.
The stem is responsible for the control of the disc. When the stem is rotated, it relays this motion to the disc by lifting or dropping it. The gate valve stem is joined to the actuator (sometimes through the yoke) or manual handling machine on the top end and the valve disc on the other end to facilitate control.
The gate valve seat is a resting point for the valve disc to which it is sealed. While some valves have one seat, the gate valve has two seats, one on each end of the pipe flanges. If the disc and valve seat are not sealed properly, it may cause leakages in the valve.
The gate valve backseat holds the stem in the valve open position. It also restricts fluid from going up to the packing chamber and the surface.
The gate valve disc is the part of the valve which performs the function of allowing or restricting flow through the pipeline. It blocks the fluid pressure from moving from one end to another. The disc rests on the valve seat to which it is sealed.
The gland packings prevent leakages from the stem and are usually in a stuffing box. The gland sleeves keep the gland packings in the box.
The yoke connects the actuator to the stem. They are sometimes merged with the bonnet to manufacture several valve designs. The yoke is also called arms.
The gate valve operation is in many ways similar to the operation of most valves. The hand wheel or actuator is controlled to rotate the stem, which controls the gate. For the handwheel, the wheel is turned in several revolutions before the gate valve can be fully open from a closed position or fully closed from an open position.
Control using the actuator is easier as it requires no user at the location, only an actuator system (pneumatic or electric) must be on site. By raising the gate to a fully open position, the valve allows the media to flow through the pipeline without obstruction.
Closing and sealing the pipe to the valve seat retains the flow pressure and restricts the flow of the media beyond the gate. The flow rate of the media experiences erratic change as the gate valve is closed, resulting in an unpredictable relationship between the valve and fluid flow rate.
Fluid pressure and flow against the gate wear out the seat and gate. Gate valves should not be used for flow regulation as the constant flow hastens the damage to the gate and seat.
Installing gate valves should be done properly to increase the service life of the gate valves and to ensure their proper operation. Here are some installation practices to be followed while installing gate valves:
Below are some essential practices to ensure the valve works effectively and lasts longer.
In selecting a gate valve suitable for operation in specific conditions, factors such as suitable material, size and design must be considered. Here are some factors to consider in buying a gate valve:
Materials used for the production of gate valves vary with specific conditions. Common materials are cast iron, cast carbon steel, stainless steel, ductile iron, gun metal, bronze, steel alloys, stainless steel, and forged steel.
Key selection criteria of material to use are fluid service and design temperature. Below are some materials used in the creation of the gate valve:
Material Grades
Below are some common trim material grades used in the production of gate valves
Trim materials are grouped and assigned a trim number or combination number. In the chart below, material for a gate valve seat, disc, stem and backseat are specified against a trim number.
From this chart, an order can be made by the trim number. There will be no need to specify any materials for an order of the gate valve trim. This chart is in line with the API 600 specification.
Source: HardHat EngineeringBelow are codes and standards that are used in the design and selection of gate valves:
API 598
API B16.34
ANSI B16.10
ANSI B16.25 and B16.11
ANSI B 1.20.1 (BSP/NPT)
This post discussed all you need to know about the gate valve, including its function, parts, installation and maintenance requirements, and what you need to consider before buying an industrial gate valve.
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