Valve Types, Applications, Components, and Accessories

The role of control valves in the industrial process loop is becoming increasingly important. As a reliable control valve manufacturer, we would like to introduce the different types of control valves, components, functions, application scenarios, and valve accessories, in a systematic and professional way in this article.

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In this section we are going to introduce a piece of brief information about control valves, in case help you to know what control valve is and which role has it played. 

What is a Control Valve?

pneumatic globe type control valves for steam system

As industrial automation processes are upgraded, more and more control valves are being used in process circuits. Almost every plant consists of hundreds of control loops. All loops are in turn networked together and used to keep a number of important process variables within defined limits to ensure the quality of the final product. These parameters include pressure, flow, temperature, level, etc. The sensors and transmitters collect the process variables to the controller, after comparing with the desired setpoints, the controller sends a corrective signal to control valves, in case modulating the valve opening to reach the required value.

In brief, a control valve is a key part of a control loop, a critical control element in industry processes, which consists of a pneumatic actuator, electric actuator, or hydraulic actuator assembly with a valve for regulating the flow capacity or temperature of fluids, or upstream pressure and downstream pressure, or level. It is widely used in petroleum, chemical, pharmaceutical, textile, paper industry, refining, oil and gas, iron and steel metallurgy, and other industries.

process control loop

Principles of Operation For Control Loop

By now we all know that the most common final control element in the process control industry is the control valve. The ultimate purpose of a control valve is to regulate the temperature, pressure, level or flow of a medium while compensating for load disturbances so that the process variable being regulated is as close to the set value as possible. The medium could be water, steam, oil, gas, or other compounds.
Typically, a control loop consists of a sensor that detects the process parameters, a transmitter, a control valve, and a controller.

open-loop control system

The sensor and transmitter collect process variables in the loop and act as an eye to monitor changes in individual parameters such as the temperature, pressure, or level of the medium. The collected value is then sent to the controller. Through the controller, which functions like a brain, the &#;process variable&#; received by the transmitter is compared with the &#;set point&#; and a corrective signal is sent to the control valve. So the control valve, as the final control element, plays the role of the hand in the control loop, making it the most important part of the automatic control system.

closed-loop control system

There are many types of control valves, each designed for specific types of applications, read this post for more details on different types of control valves.

globe type control valves &#; THINKTANK

Globe type control valve is the most common final control element during the process loop, and it gets its name as its spherical shape. According to the ports of the globe valve body, it includes 2-way control, 3-way mixing control, and 3-way diverting type.

globe type control valve drawing

Butterfly Type Control Valves

When we talk about butterfly control valves, we generally refer to high-performance butterfly valves (double eccentric butterfly valves) and triple eccentric butterfly valves (triple offset butterfly valves).

offset technology for butterfly valves

In most applications, butterfly valves can replace other types of control valves because they provide the same basic functions, but often have more safety features and better performance. Using butterfly valves in your application can reduce maintenance requirements, improve the accuracy of flow control, and reduce the risk of disasters such as leakage. Butterfly control valves are also used to control water treatment plants because they provide the best seal and can withstand water pressure. Especially in large-diameter pipelines, the use of butterfly control valves is cost-effective.   

control butterfly valves type

Segmented Ball Type Control Valves

The v-port or segmented ball is the most common type for ball control valves. Ball valves are widely used in fluid systems in many industries due to their low cost, durability, and excellent closing performance. Similar to butterfly valves, they are not as effective in flow control applications that require high precision and control sensitivity. One of the reasons is that the ball valve requires high torque to open and close, which prevents the operator from making fine adjustments. There is also a certain gap between the stem and the ball, which makes it difficult to find a specific flow rate suitable for fluid control applications.

eccentric plug rotary control valves drawing

The eccentric rotary valve is an innovative technology that combines many of the ruggedness, compactness, and long-stem seal life of globe valves with simplicity and reliability.

eccentric plug pneumatic control valve

The eccentric plug rotary control valves have two offset for construction design. One is the shaft is offset behind the valve seat and the other is the shaft is offset from the centerline of the valve. 

eccentric plug valve6

When the valve shaft and plug of the eccentric plug control valve start to move, the plug cams away forward open from the seat once the valve just started. There is no friction between the plug and the seat. 

Reduced Trim Full Ball Valve

The reduced trim full ball valve is the design that has a triangular window on side of the ball. 

reduced trim full ball valve

This reduced trim ball valve is not commonly used in initial selection and sizing, most applications are when you find after the plant starts up that a ball control valve is oversized, the capacity is way large than the process required, so if you are not able to alter the piping to accommodate the smaller size valve and the necessary piping reducers, then reduced trim full ball valve is your best choice. 

Most of the flow path windows are triangular or V-shaped to get as close as possible to the inherent flow characteristics of EQ%. The wide width of the window determines the maximum flow capacity of the control valve.

Globe Control Valves vs. V-Port Ball Control Valves

ItemGlobe Type Control ValveV-Port Ball ValveFunction2-Way Flow Control Valve
3-Way Mixing Type Control Valve
3-Way Diverting Type Control Valve2-Way Flow Control ValveShutoff TightnessNot Zero LeakagePositive Shutoff, Zero LeakageControl AccuracyExcellenceCoarseHigh Response CycleYes, Constant ControlNoFlow CapacityLowerHigherCavitation PreventionPriority Selection&#;High TemperaturePriority Selection&#;Easy MaintenancePriority Selection&#;Cost&#; More Economical Solution

Component for Control Valves

There are two major types of control valves, linear and rotary motion. The rotary type control valve is a quarter-turn motion, and the linear type control valve is a sliding motion. So we will separate those two types and list each component for control valves.

Linear Motion Control Valve (Globe Type) 

what are the different types of control valves in industries

Above is a cross-sectional view of a globe type control valve, which clearly shows the main components. globe type control valves can also be called sliding globe type control valves. 

1. Valve body
   The valve body is the main part of the control valve, which is the channel to carry the fluid pressure and control the variable parameters. The valve body is the main component of the control valve and is the channel that carries the fluid pressure and control variables.
2. Bonnet
   The bonnet is the part of the valve that carries the pressure and keeps the valve body and stem sealed by the stem seal packing. As a globe type control valve, the bonnet is bolted to the valve body to facilitate the assembly of the valve internals. This type of bonnet is also known as a bolted bonnet design, as opposed to the integral cast bonnet of most rotary valves. 
3. Trim
   The valve trim generally consists of a stem, plug, and seat.
   The stem is used to connect the actuator to the plug.
   The plug is the movable element that is assembled in the flow path to change the flow of the medium through the valve.
   The seat is fixed to the valve body and together with the plug forms the fluid passage while providing a contact surface for the plug to close the flow.

Rotary Motion Control Valve (Butterfly Type and Ball Type) 

assembly butterfly valves

Rotary control valves are also known as quarter-turn control valves, and the definition of each part is similar to that of linear type control valves. Only the name of the bonnet is different. The bonnet of almost all rotary valves is cast as a part of the valve body as an entirety and is usually called an &#;integral bonnet&#;. Instead, the bonnet is bolted to the valve body as in the case of globe valves.

The part that connects the actuator to the closure element is called a stem by some manufacturers, and a shaft by others.

The closure element of a butterfly valve is called a disc, while a ball valve is called a sphere or ball.

Accessories

Actuator

The actuator for the control valve is a mechanical device that uses an external power to modulate valves.

valve actuator symbols

There are four different types of actuators for the control valve, pneumatic actuator, electric actuator, hydraulic actuator, and self-operated actuator. An actuator is an important component for control valves, which drive to open or close valve. For the industrial process control loop, pneumatic and electric actuated are the most common types.  

Pneumatic Actuator

The pneumatic actuator includes a multi-spring diaphragm pneumatic actuator, single-spring diaphragm pneumatic actuator, sing-acting and double-acting piston/cylinder pneumatic actuator, and rotary type pneumatic actuator(rack&pinion, and scotch yoke).

1. Multi-Spring Diaphragm Pneumatic Actuator

The multi-spring membrane pneumatic actuators of spring return type are applied for control operation of control valves, and other positioning elements in industrial automatic systems. There are two following design options for the actuator:

multi-spring diaphragm actuator

• Direct action (air &#; advances the steam)
• Reverse action (air &#; retracts the steam)

direct-acting diaphragm pneumatic actuator

(a) Direct-acting (PZMA)

1. Upper diaphragm castings
2. Diaphragm
3. Diaphragm plate
4. Spring
5. Down diaphragm castings
6. Actuator stem
7. Yoke
8. Adjust nut
9. Travel indicator

reverse acting diaphragm pneumatic actuator

(b) Reverse-acting (PZMB)

1. Upper diaphragm castings
2. Diaphragm
3. Diaphragm plate
4. Spring
5. Down diaphragm castings
6. Actuator stem
7. Yoke
8. Adjust nut
9. Travel indicator

2. Single-Spring Diaphragm Pneumatic Actuator

Diaphragm Actuator 657 Single Spring

3. Linear Piston/Cylinder Pneumatic Actuator

linear type pneumatic actuator

4. Rotary Type Pneumatic Actuator

rack&pinion pneumatic actuatorscotch yoke pneumatic actuator

How to select the right actuator for your application?

We know that an automated control valve needs an actuator to operate the valve, pneumatic actuator and electric actuator are different, so it may cause confusion when you select an actuator for your application. The following step-by-step method can help you figure out which actuator is exactly perfect for your condition.

Step 1: Check the valve type

Linear type control valve

electric control valves for power plantelectric globe type control valves

Linear type control valve includes globe type, gate type, and pinch valve. The actuator assembly for these control valves must provide linear motion to operation.  

control valves manufacturerpneumatic angle type control valves with smart positioner

Rotary type control valve

The rotary type control valve applies the actuator produces the rotational motion to operate a valve. Eccentric plug valve, butterfly valve, segment ball Valve, and full port ball valve are all categories by rotary type control valve.

electric butterfly control valveseccentric plug valve7shutoff butterfly valveshigh performance butterfly valves1

Electric actuators have high levels of precision, control, and energy efficiency. They are usually used for on/off control with fail in the last valve position. And its cost is more expensive than pneumatic rotary actuators.

Pneumatic rotary actuators are known for fewer and simple components, so it makes easier and cheap for maintenance work. Pneumatic actuators with spring return are very commonly used for the failsafe condition, such as FC(fail to close valve) or FO(fail to open valve).

Step 2: Check the available power source on your site

This is a key issue if the site can only provide electric power, not equipped with external air source equipment, in order to save costs, generally use an electric control valve. On the contrary, if equipped with sufficient air supply, then pneumatic control valves are a better option for the process loop.

Pneumatic diaphragm actuators usually required an airpower range of 1.4 bar to 4.5 bar, and piston-type pneumatic actuators required 3 bar to 10 bar power. It&#;s difficult for plants to guarantee above 6bar at all times for the process equipment, it&#;s one of the reasons why diaphragm actuators are so commonly assembled for control valves. If low airpower which under 5 bar will require a large size of pistons to generate torque to operate valves. 

Piston pneumatic actuators are available in two main types: rack&pinion, and scotch yoke.

Both of these rotary pneumatic actuator types provide a compact and economical solution for quarter-turn(90-degree) full port ball valves, eccentric plug control valves, high-performance butterfly valves, and segment ball valves.

In many plants, electric actuators are commonly available power voltages with 12 and 24 VDC, and 24, 120, and 220 VAC, 1-phase. For power plants, most use 380V, and 400V 3-phase power. 

Step 3: Installation Space

control valves for boiler3control valves for boiler6

Usually, in complex piping systems, we need to consider the installation space of the control valve, for the narrow installation space, the engineer needs to first consider the compact rotary type control valve, such as eccentric plug control valve, segment ball valve, and butterfly control valve.

Step 4: Function

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Most engineering has requirements for actuator function, such as on/off or modulating, service cycle life, failure position, operating speed, control accuracy, assemble with manual operator/handwheel, local control, or others. 

We also need to consider the media characteristics if it&#;s flammable, then pneumatic actuators are safer than electric actuators. So pneumatic actuators are very commonly used in hazardous or explosive working areas, however, any electrical accessories such as limit switch, valve positioner, and solenoid valve assemble for pneumatic actuator still need to meet NEMA standards. 

The electric actuator also can be used in hazardous areas, just more expensive than the pneumatic actuator. Just need electrical components and enclosure to meet the NEMA standards. 

Step 5: Environmental conditions or ambient temperature

General pneumatic actuators can handle temperature ranges between -4°F to 175°F, due to the piston seal ring, bearing, and mounting design can&#;t bear high temperatures.

Since low-temperature environments can cause air sources to condense, the condensate may freeze and block the air supply tube, causing the pneumatic actuator to fail to operate.
Electric actuators can be used in the temperature range of -40 to 150°F, but are also affected by ambient temperature and humidity. When used outdoors, electric actuators should be rated for that environment to prevent moisture buildup from damaging electrical components. Also in outdoor low-temperature environments, the heat from the motor can cause condensation to form on the electric actuator housing, so the actuator should be fitted with thermostat accessories or a heater to maintain a constant temperature and avoid the occurrence of condensation issues.

Step 6: Budget

In general, the cost for globe type control valve is higher than rotary type control valve, such as butterfly type and ball type.

electric actuated control valve

The electrical actuator is mounted on the control valve which uses an electromagnetic device converts electrical energy into mechanical movement, it uses an external power source like 220VDC, 24VAC, 380V, or other power voltage to drive valves. Most electrical actuators use limit switches to turn the motor off when the actuator reaches the final valve position, due to it is activated by cams that are mounted on the stem drive shaft.

Electric actuators can be classified as linear and rotary electrical actuators. 

The linear electrical actuator also called motorized valve actuator, which commonly used for globe type control valves. For rising stem control valves assemble electric actuators to operate with a screw drive. The closure element of the valve is moved up and down by the rotation of a threaded rod that is connected to the valve stem. 

Valve Positioner

• Mechanical electro-pneumatic positioner 
• Mechanical pneumatic-pneumatic positioner
• Digital valve positioner
• Smart valve positioner

Limit Switch

A limit switch for control valves is a device designed to provide a valve position signal to the controller, such as PLC or DCS control system. This accessory can be integral to an electrical actuator and be separately assembled into a pneumatic actuator or valve yoke.

Generally, there are two common types of limit switches used for control valves regarding valve movement.

For sliding stem/linear type control valve, these limit switches are assembled at the valve stem and enable the signal of valve opening or close position to the control system. Some conditions only require one signal of valve closing or opening to the controller, but some require both positions, valve close, and valve open position. 

control valve with 2pcs limit switcheslimit switch for control valves

Two available options:

1. 1PC limit switch assembly for linear type control valves, signaling valve close, or valve open position.
2. 2PCS limit switches assembly for linear type control valves, signaling valve close, and valve open position.

For rotary type control valves, like ball valve, butterfly valve, and eccentric plug rotary control valve, they use a limit switches box, which has a visual indication of the valve position. The limit switches box is typically activated by cams connected to the shaft and equipped on the pneumatic actuator to the control valve. 

pneumatic butterfly valves

Limit switches send electrical feedback from two micro switches to indicate valve position. Typically for on/off type control valve, which confirms either open or close position in site.

Solenoid Valve

Solenoid valve is equipped with pneumatic control globe valves that main function is to lock the valve at the last valve position, and also it can vent out the air from the pneumatic actuator, in case drive valve to the safe position.

Lockup Valve

globe type control valve ss material 2

I/P Transducers

I/P transducer means making a current signal 4-20mA converts proportional pressure output of 3-15psi. This accessory is used for an application that does not require a high level of positioner accuracy of a positioner, only needs an electro-pneumatic sensor to transfer the signal. 

Air Filter Regulator

An air filter regulator is a necessary accessory for the control valve, usually assembly before the actuator, in case the air power reduces the right pressure range for the pneumatic actuator. For example, if the diaphragm pneumatic actuator requires 2.4bar air power, then we need to adjust the air filter regulator to reduce the pressure to meet 2.4bar, otherwise, the air power will damage the diaphragm. Also, it can filter the Impurities in the air.

Volume Booster

Volume booster is used for large volume needed pneumatic actuator, the airpower is not enough to provide large air volume in a short time, so in case of speed up the response of control valve, volume booster can provide extra pneumatic thrust output capacity to the valve.

Typically single-acting pneumatic actuators only request one volume booster, and double-acting pneumatic actuators require at least two sets. 

Quick Exhaust Valve

Compressed air flows from the control valve and through the quick exhaust valve to the cylinder, speeding up the opening time of the valve.

Position Transmitter

Sometimes control valve required a positioner transmitter that can send a 4-20mA output signal to control system, in case to feedback a actual valve position.

Manual Operator

A manual operator is an additional handwheel for the control valve, in the case of an emergency situation we can operate by a manual operator.

There are three types of manual operators for control valves.

1. Top-mounted handwheel (Usually for linear type pneumatic actuator)
2. Side-mounted handwheel&#;Either linear or rotary type pneumatic actuator)
3. Gear Operated handwheel (For rotary type control valves, such as ball, eccentric plug, or butterfly valves)

1. Top-mounted handwheel2. Side-mounted handwheel3. Gear operated handwheel

The Installation Layout of the Control Valve

the layout of installation control valves

Valve Types and Typical Applications

Valve TypeIsolationModulatingPressure ReliefDirectional ChangeGateR×××GlobeRR×R(note 1)Check(note 2)×××Stop CheckR×××ButterflyRR××BallR(note 3)×R(note 4)PlugR(note 3)×R (note 4)DiaphragmR×××Safety Relief××R×R: Recommended x: Not Recommended

Notes

1. Only angle-type globe control valves can be used for a 90-degree change in direction of flow.
2. Check valves (non-return valves) reverse flow only in one direction. Stop check valves can be and are functional as stop, block, or isolation valves, also being used as a check valve.
3. Some designs of ball type and plug valves are suitable for modulating service, it depends on the manufacturing design. 
4. Multi-port ball valves and plug valves are used for changing the direction of flow and mixing flows.

Learn the Best Type of Flow Control Valve for Your Application

There are many different types of flow control valves that can be used in a variety of industries. Some valves are complex enough to adjust automatically to pressure and temperature variations, which is why they are called flow control valves. Regardless of their construction, flow control valves are designed to modulate the flow capacity or pressure of fluids, and they respond to signals from flow meters, senses, and transmitters.

Valve TypeTop-Guided Globe ValveCage-Guided Globe ValveFull Port/Segment Ball ValveEccentric Plug Rotary Control ValveHigh-Performance Butterfly BudgetHighHighMedium MediumLowFlow Capacity vs. Globe Control 1x1x2x1x2xCavitation Potential LowLowMedium MediumHighCavitation/Noise Reduction OptionNoYesSomeSomeNoInherent Flow CharacteristicEQ%, Linear, Quick OpeningEQ%, Linear, Quick OpeningEQ%, Quick OpeningModified LinearModified EQ%Suitable for High Pressure DropLimited YesLimitedYesLimitedSuitable for SlurriesLimitedNoYesYesLimitedWeightHighHighMedium MediumLow

Basic Terminology of Control Valves and Explanations

Flow Coefficient Cv

The control valve flow coefficient Cv is the flow rate in Gallons Per Minute of 60°F pure water when there is a pressure differential of 1 PSI through the valve at specified travel.

The control valve flow coefficient Cv is the flow rate in Gallons Per Minute of 60°F pure water when there is a pressure differential of 1 PSI through the valve at specified travel.

where:
Q is the rate of flow (expressed in US gallons per minute)
SG is the specific gravity of the fluid (for water = 1)
ΔP is the pressure drop across the valve (expressed in psi).

Here are some numbers that show you relatively how much flow capacity will go flowing through the control valve. For example, a control valve with a Cv rate of 100 will go flowing through 250GPM. Under the same process conditions, a Cv of 200 will go flowing through 500GPM, and a Cv of 300 will go flowing through 750GPM.

Cv 100 = 250GPM
Cv 200 = 500GPM
Cv 300 = 750GPM

So we know the bigger of Cv rate, we got the larger the flow capacity. Typically, doubling the size of the valve will increase the Cv about three to four times.

Class IBy agreement between user and supplierClass II0.5% of rated valve capacityClass III0.1% of rated valve capacityClass IV0.01% of rated valve capacityClass V5×10-4 ml per minute water/inch seat dia./psi of pressure differentialClass VIA small number of bubbles per minute depending on seat diameter

During the selection process of a control valve, we all need to confirm the flow characteristics required for the valve. As a valve manufacturer, we do not know what kind of system this control valve will be installed in (except for the complete solution), so generally, we only provide the inherent flow characteristics which are the relationship between valve opening and flow rate.
In fact, a control valve has two characteristics, one is the inherent flow characteristics, and the other is installed flow characteristics. The end-user is often concerned with the installed flow characteristic which is the relationship between the control valve opening and the flow rate in the particular system being installed.

Cavitation Potential 

Cavitation is a very serious problem that could break the control valve performance. The pressure recovery factor of control valve FL represents its tendency to cause cavitation problems. Generally, the higher capacity of rotary valves has a higher recovery factor that has a greater tendency to cavitate. But it doesn&#;t mean butterfly valves, eccentric plug rotary control valves, segment ball control valves, and other rotary type control valves are not good for modulating function.  However, we need to pay more attention that these valves are selected and sized right. 

There are many specifications that will tendencies valve cavitation, different valve type has different tendencies, despite they have a low FL but still have a greater potential for cavitation.

cavitation damage

In conclusion, the selection and calculation of control valves need to consider many factors, the above content can not display all the knowledge, but we will continue to update the content as much as possible, at the same time, if you are interested in the calculation formula and sizing information, you can go to our download page for free download.

THINKTANK is a reliable valve manufacturer in China, which focuses on control valves and self-operated pressure regulators. All products are CE, SIL3, and ISO- certified, and the quality and service are guaranteed.

We&#;re based in Taipei of Taiwan since and offer OEM and ODM services for 42 international brands and deeply cooperate with 35 countries&#; valve distributors and engineering.

THINKTANK&#;s quality, competitive prices, and superior services make it the best valve partner to help you grow your business. We&#;re qualified with ABB, Siemens, and Bray.

Please do not hesitate to contact us on 21 , WeChat +86 189 , Skype ID sowell85, +86 185 , or marketing at cncontrol valve.com

Introduction to Valve Part Fundamentals

Industrial valves are made up of many different components that allow them to regulate flow. The main parts of a valve designs can be divided into the body, trim, actuators, and ancillary accessories. This table provides a brief overview of the primary valve components and their functions:

Valve PartDescriptionValve BodyThe main pressure boundary of a valve that contains the flow. Usually made of cast or forged metal.BonnetThe cover that allows access to the valve internals for assembly and maintenance. Bolted, threaded, or welded to the body.TrimThe internal moving components that modulate the flow, such as the disc, ball, plug, or gate.SeatThe stationary surface against which the movable trim seals off flow. Precision machined based on trim type.StemThe component that connects the actuator to the trim, allowing motion to control flow.PackingCompressible rings that seal around the valve stem to prevent leakage. Requires periodic replacement.GasketUsed to seal non-moving parts, like between the bonnet and body. Provides high integrity seal.ActuatorProvides the force to open and close the valve&#;s internal parts. Can be manual, pneumatic, hydraulic or electric.PositionerControls the actuator so the valve moves to the precise flow control position demanded.Limit SwitchesFeedback devices to indicate open and closed position for monitoring.Gear OperatorsGears that allow manual handwheels or actuators to produce high valve torques with lower input effort.

Valve Bodies &#; The Pressure Containment Shell

The valve body, also called the shell, housing, or casing, is the primary pressure boundary of a valve. It serves as the framework that holds together all the other valve parts in proper alignment. Valve bodies are designed to withstand pipeline pressure, temperature, and mechanical stresses. The inlet and outlet of the valve body connect to the piping system. There are various body styles and configurations, with the most common being globular, straight-through, angle, and Y-pattern. The body shape depends on the valve&#;s intended flow control function. Gate, globe, check, ball, plug, and butterfly valves all have distinctive body designs tailored to their unique flow control application. Valve bodies are cast or fabricated from materials like carbon steel, stainless steel, cast iron, alloy steel, and forged steel. The material is chosen based on the process fluid composition, pressure, and temperature. Many valve bodies have flanged ends to enable connection to piping. Others may have threaded, socket weld, or butt weld ends. No matter the style, the valve body must be strong enough to withstand the system pressure when the valve is in the closed position. It must also be rigid and resistant to warping or cracking that could cause leaks.

Valve Body Materials for Different Services

There are various options when selecting valve body materials based on the service conditions. Carbon steel is suitable for water, oil, and gas service. Stainless steel handles more corrosive fluids like acids or wet chlorine gas. For extremely high temperatures, alloy steel and cast iron are better choices. Cryogenic valves for frigid liquids like LNG use stainless steel or forged carbon steel bodies. The body material also affects maintenance requirements. For example, carbon steel is prone to rusting or corrosion over time and may need frequent repairs. Stainless steel and alloy steel have higher corrosion resistance, extending the service life. In highly abrasive applications, a hardened valve body is required to resist wearing. No single material is ideal for all applications. Consider fluid composition, pressure, temperature ranges, and desired valve life when choosing a body material. Partnering with an experienced valve supplier is key to getting the right metal for reliable service.

Valve Bonnet Styles for Access and Assembly

The valve bonnet is the cover on the upstream side that completes the pressure shell of a valve body. It also provides the means for assembling the internal valve parts and accessing them for maintenance. There are three main bonnet configurations: screw, bolted, and welded. A screw bonnet has threads that engage with the body and provides a compact means of assembly. It is easy to open and close for routine inspection and repairs. Bolted bonnets have a separate flanged head that connects to the body using long bolts. This allows very large valves to be assembled in sections. Bolted bonnets are common on gate, globe, and check valves over NPS 2. Welded bonnets have the cover permanently welded to the body. No threads or bolts are used, creating a tight seal. However, this does not allow accessing internal parts without cutting. Welded bonnets are preferred for high pressure and temperature systems where bolts or threads could leak. They also cost less than bolted styles. When selecting a bonnet type, consider the maintenance needs, potential leakage risks, valve size, and expense. The bonnet must withstand system pressure and temperature fluctuations. Leak-proof, easy disassembly and assembly is ideal for most applications.

Trim Materials for Erosive and Corrosive Fluids

Valve trim refers to the internal moving parts that modulate flow such as balls, plugs, discs, and gates. The trim comes in contact with the process fluid, so its material must handle the chemical, temperature, and abrasive characteristics. Hardened trim materials include tungsten carbide, Stellite alloys, titanium, Inconel high-nickel alloys, and 440C stainless steel. These withstand highly erosive or corrosive substances. Softer trim materials like bronze, aluminum, Monel, and 304 stainless suit less destructive fluids. The trim material really depends on the fluid composition. For example, a high nickel alloy is better for hydrofluoric acid compared to regular stainless steel. Cryogenic valves need trim that handles freezing temperate without becoming brittle. Abrasive slurries require durable trim that resists wearing. Partnering with an experienced supplier is key to getting the right trim materials for your specific process conditions. This ensures long service life and minimal erosion damage.

Valve Packing vs. Gasket Sealing Methods

Valves use sealing systems to prevent fluid leakage between the stationary body and moving parts. Packing and gaskets are the two main sealing methods. Valve packing consists of rings made of soft, deformable material like graphite, PTFE, or flexible graphite. The rings fit around the valve stem and compress when the bonnet or gland follower tightens. The soft packing deforms to create a tight seal. Packing can leak over time and must be periodically tightened or replaced. It allows some controlled leakage for lubrication. Gaskets provide a more permanent seal between two mating surfaces. Common types are spiral-wound metal, ring joint, kammprofile, and flat paper or plastic. Gaskets require more precision machining for leak-proof performance. Packing handles frequent disassembly better since gaskets can be damaged during maintenance. For fugitive emissions control, metal gaskets are preferred over packing. However, packing enables easy stem movement and regular adjustment. Consider maintenance needs, allowable leakage, and emission regulations when choosing packing or gasket seals.

Flexible vs Solid Wedge Gate Designs

Gate valves use linear motion gates to start and stop flow. The gate and valve disk can be flexible or solid. Flexible wedge gates have a solid top edge but flexible sides made of metal bellows or laminated sheets. This allows the gate to match the bore when seating, creating a tight seal even on worn valve seats. However, bellows can burst or laminations separate after frequent flexing. Solid wedge gates are a one-piece solid gate that cannot flex. These provide a sturdier gate but require precision machining for effective sealing without leakage. Solid wedges are better for high pressure or frequent operation. Flexible gates suit low pressure modulating control where tight shutoff is needed. Gates must be resistant to cutting, scoring, and deformation from fluids. Flexible gates suit liquids and clean gases. Solid gates work for steam, gases with solids, and contaminated fluids where a bellows could rupture. Consider shutoff requirements, pressure, media properties, and desired service life when choosing between flexible and solid gate designs.

Rising and Non-Rising Valve Stems

The valve stem translates motion from the actuator to the flow controlling element inside the valve. It may have a rising or non-rising design. Non-rising stems remain vertical as the valve operates. The stem is threaded into the gate, plug, or ball and turns it without lifting. Rising stems lift up and down with valve motion while remaining attached to the flow control element. Rising stems indicate valve position and can automate control via positioners. Non-rising stems require separate shaft position indicators. Rising stems are common on gate and globe valves. Non-rising stems suit ball and plug valves where turning motion is required. Non-rising stems work well for buried valves or corrosive fluids where rising stems could get damaged or cause binding. The stem must align with the actuator and match its torque output. Consider maintenance needs, automation requirements, and environments when selecting between rising and non-rising stem designs.

Purpose and Use of Valve Backseats

The backseat is a wearing surface on the valve stem that contacts the bonnet when the valve is fully open. It serves several purposes. First, it provides an additional seal between the stem and bonnet. This isolates the bonnet from system pressure when doing maintenance. It also gives the valve a bidirectional shutoff ability &#; seal both upstream and downstream. Backseats also enable packing adjustment and replacement while the valve is pressurized. Finally, backseats can act as a stopping point when fully open, preventing damage to seating surfaces. Backseats are common on gate, globe, and check valves. They should have enough surface area to prevent excessive wear. Stainless steel, brass, or carbon graphite materials work well. Consider whether backseats would facilitate safer maintenance when selecting valves. But they aren&#;t recommended for infrequently operated emergency shutoff valves.

Types of Valve Actuators: Linear, Quarter-Turn, Multi-Turn

Actuators provide the force to open, close, and position the valve. Common types are linear actuators, quarter-turn actuators, and multi-turn actuators. Linear actuators apply thrust along the stem&#;s axis to drive gates, globes, or diaphragms up and down. These are often pneumatic cylinders or hydraulic pistons. Quarter-turn actuators rotate 90 degrees to open/close ball, plug, and butterfly valves. Manual lever arms, electric motors, or pneumatic cylinders are common quarter-turn actuators. Multi-turn actuators use gearing to allow for multiple 360 degree rotations. These automate precise positioning of globe and gate control valves. Another benefit of gearing is the high output torque from a small electric motor or manual handwheel. When selecting valve actuators, consider torque requirements, speed, automation needs, space constraints, and hazardous area rating. The actuator output must match the torque demands of the valve, especially for 100% shutoff.

Valve Components Selection for Special Use Conditions

Valves contain many components, and material choices depend on the application. For steam systems, metal seats, bonnets, and steam-rated packing suit the high temperature and avoid oxidation. In cryogenic applications, the body, trim, and seals require materials that stay ductile at freezing temperatures like stainless steel. Highly corrosive fluids need stainless steel or alloy bodies and trim along with corrosion inhibiting sealant on gaskets. For throttling control valves, components supporting smooth stem movement and flow characterization are essential. This includes characterized trims, modified trim geometry, low-friction packings, and high resolution actuators. The principles are the same, but components must be tailored to safely handle the operating conditions. Partnering with an experienced supplier ensures that all valve parts are suited to the service.

How to Select Parts of a Valve Correctly

Properly selecting valve components requires careful consideration of the service conditions, performance requirements, and desired valve type. Here are some important considerations when choosing valve parts:

For welding end valves, ensure the valve-body ends and weld joint design suit the piping system and materials. Flow mediums that require tight shutoff may need metal-seated ball valves with properly matched stem threads, outside screw and yokes that prevent side loading. High pressure applications need sturdy valve bonnets, thick stem packing in the stuffing box, and sturdy yoke bushings.

Relief valves require precise trim parts and trim designs to provide accurate pressure control. Ball valves used for throttling duties require characterized ball and seats to control flow. The rotational motion of ball and plug valves depends on quality bearings and seals internal elements.

Control valves rely on valves bonnets, gaskets, stem packings and other parts to prevent leakage and enable smooth actuation. The top of the yoke and downstream side covers of a swing-check valve see the most wear, so durable materials are vital.

Choosing control valves also means matching the actuator style and output to provide the right type of motion &#; rotary for 90 degree ball valves or linear for globe designs. This ensures proper valve positioning and tight shutoff when closed.

No matter the valve type, considering spacing, installation, and maintenance requirements will guide the selection of compact wafer, lugged, or flanged designs. Partnering with experienced suppliers and following PMI standards ensures the parts selected provide long service life.

Conclusion

Understanding how the various internal parts of valves work together is critical for engineers, maintenance staff, and plant operators. The body, bonnet, trim, stem, seals, and actuators all play a role in controlling fluid flow safely and reliably. Component selections must be based on service conditions and performance goals. With the right knowledge of component functions and material differences, industrial valves can be kept in prime operating condition for their essential role in managing fluids.

Contact us to discuss your requirements of Automation Components. Our experienced sales team can help you identify the options that best suit your needs.