Butterfly valves can be used for a wide range of applications such as water supply, wastewater treatment, fire protection, the chemical and oil industries, fuel handling systems, and also for applications within the power generation industry.

With the introduction of the double and triple eccentric designs, butterfly valves are more and more used also in the oil and gas industry and have started to compete with more traditional valves, such as globe and ball valves.

Butterfly valves are comprised of several key components that allow them to effectively control fluid flow. Each part plays a crucial role in the valve’s operation, durability, and ability to provide a tight seal.

Here are the main components of a butterfly valve:

1. Body

The outer casing of the valve holds all internal components together and connects the valve to the piping system. The body material varies depending on the application and can include cast iron, stainless steel, PVC, and others.

2. Disc

The circular element that pivots within the flow stream to open or close the valve. The disc’s rotation controls the flow through the valve. Materials for the disc often match or are compatible with the body material and are selected based on the fluid’s properties.

3. Stem

The shaft that connects the disc to the actuator or handle outside the valve body. The stem can be one-piece with the disc or two-piece, where the disc is mounted between two stems. Stems are typically made from stainless steel or other corrosion-resistant materials.

4. Seat

The sealing surface against which the disc closes. The seat can be integral to the valve body or a replaceable component. It is made from materials like rubber, PTFE, or metal, depending on the application’s sealing requirements and the fluid’s characteristics.

5. Actuator

The mechanism used to rotate the disc. Actuators can be manual (handles or gears) or automatic (pneumatic, hydraulic, or electric). The choice of actuator depends on the valve size, required control level, and operational environment.

6. Handle or Hand Lever

For manual operation, a handle or lever is attached to the stem, allowing the operator to rotate the disc. It usually includes a locking mechanism to secure the valve in the open or closed position.

7. Gearbox

In larger butterfly valves or in applications requiring precise control, a gearbox is used in conjunction with the hand lever or actuator to facilitate easier operation by reducing the effort needed to turn the valve.

8. Bushings

Located between the stem and the body or between the stem and the disc, bushings reduce friction and wear during operation, contributing to the valve’s smooth operation and longevity.

9. Packing

A seal around the stem to prevent fluid from leaking out of the valve body along the stem. Packing materials vary but often include PTFE or graphite, chosen for their sealing properties and resistance to the process fluid.

10. Flanges or Ends

Butterfly valves can have different end configurations to connect to the piping system, including wafer, lug, flanged, or butt-weld ends. The selection depends on the piping system design and the requirements for disassembly and maintenance.

Each component of a butterfly valve is critical to its performance, affecting everything from how well the valve seals to how easily it can be operated and maintained. Selecting the right materials and design for these components is essential to ensure the valve meets the application’s demands.

The pressure drop across a butterfly valve, like other control valves, is an essential factor to consider in system design and valve selection. Pressure drop refers to the reduction in pressure as fluid passes through a valve, a phenomenon that occurs due to friction and flow resistance introduced by the valve’s presence in the flow path.

Factors Affecting Pressure Drop in Butterfly Valves

1. Valve Design: The inherent design of butterfly valves, which includes a disc that pivots within the flow stream, inherently introduces some level of flow resistance. The size of the valve (relative to the pipe diameter), the disc shape, and the seat design can influence the extent of this resistance.

2. Disc Position: The pressure drop is significantly influenced by the disc’s position. When fully open (parallel to the flow direction), the pressure drop is minimal. However, as the disc begins to close (rotating towards a perpendicular position to the flow), it increasingly obstructs the flow path, leading to a higher pressure drop.

3. Flow Rate: The rate at which fluid flows through the valve directly affects the pressure drop; higher flow rates generally result in higher pressure drops due to increased friction and turbulence around the disc and within the valve body.

4. Fluid Properties: The type of fluid (its density and viscosity) also impacts the pressure drop. More viscous fluids tend to create higher pressure drops compared to less viscous ones under the same conditions.

Calculating Pressure Drop

The pressure drop across a butterfly valve can be calculated using various formulas and coefficients that account for the factors mentioned above. One common method involves using the valve’s flow coefficient (Cv) for a given valve opening position. The Cv value represents the flow rate of water (in US gallons per minute) at a temperature of 60°F that will flow through the valve with a pressure drop of 1 psi.

The general formula to estimate the pressure drop ($\Delta P$) in psi is:

Where Q is the flow rate through the valve in US gallons per minute (GPM), and Cv is the flow coefficient of the valve at the specific opening position.

Considerations for System Design

• Selection: Choose a valve size and type that minimizes the pressure drop consistent with the application’s requirements. Full-port (or full-bore) butterfly valves generally offer lower pressure drops.
• Operation: Understand that frequent operation near the closed position increases the pressure drop and can impact pump performance and energy consumption.
• Application: In applications sensitive to pressure drop, consider the valve’s impact on the overall system and evaluate if an alternative valve type or size might be more appropriate.

In summary, while butterfly valves are favored for their compact design and quick operation, their influence on system pressure must be considered, especially in applications where maintaining pressure is critical. Proper valve selection and system design can help manage pressure drops to acceptable levels.

BUTTERFLY VALVE SPECIFICATIONS (ASME/API)

MATERIALS FOR BUTTERFLY VALVES

VALVE BODY

Butterfly valves, like any other type of valve, are available in multiple material grades and combinations of materials (body, disc, seat).

The selection of the materials is based on the fluid to be shut off, the pressure, and the temperature of the application at hand.

The body material of a butterfly valve is a critical factor that determines its suitability for specific applications, especially considering the fluid it will handle, the operating environment, pressure, and temperature conditions. Various materials are used for butterfly valve bodies, each offering different properties in terms of strength, corrosion resistance, and cost.

Here is a list of the main materials used for butterfly valve bodies, which are generally cast grades.

CAST IRON

• Properties: Good mechanical strength, excellent vibration and shock resistance, and cost-effectiveness.
• Applications: Widely used in water and wastewater treatment, air conditioning systems, and other low to medium-pressure applications.

CARBON STEEL

Carbon steel is the most common material for body and disc in oil & gas applications:

• Properties: High strength and durability, with good resistance to high pressure and temperature.
• Applications: Used in oil and gas, power generation, and other industrial applications where high-pressure and temperature resistance is required.

The most common grades used for butterfly valve bodies and discs are ASTM A216 WCB and LCC (Low Carbon Content), which are both cast types. They are used, respectively, for high-temperature and low-temperature service.

The main advantage of carbon steel (CS) butterfly valves is their relatively low cost combined with acceptable performance (especially for low-pressure applications). The weakness of carbon steel valves is their poor resistance to corrosion (which can be improved by applying external paints or internal lining materials such as Teflon)

STAINLESS STEEL

Stainless steel butterfly valves are widely utilized across various industries for their durability, corrosion resistance, and suitability for handling a broad range of fluids, including corrosive substances, water, steam, and gas. Constructed from stainless steel for both the body and the disc, these valves offer several advantages and are chosen for specific applications based on their material properties.

Advantages of Stainless Steel Butterfly Valves

• Corrosion Resistance: Stainless steel offers excellent resistance to corrosion caused by various chemicals and environmental conditions. This makes it ideal for applications in chemical processing, pharmaceuticals, and food and beverage industries, where maintaining purity is critical.
• High Strength and Durability: Provides strength and durability under high-pressure conditions, ensuring a long service life even in demanding applications.
• Temperature Resistance: Capable of withstanding both high and low temperatures, making them suitable for applications involving steam, hot fluids, or cold water systems.
• Hygienic Properties: The smooth, non-porous surface of stainless steel is easy to clean and disinfect, which is essential for sanitary applications in the food, beverage, and pharmaceutical industries.
• Aesthetic Appearance: Stainless steel has a clean and modern appearance, which is often preferred in visible installations.

Common Grades of Stainless Steel for Butterfly Valves

• 304 Stainless Steel: Offers good corrosion resistance and is widely used in general applications that do not involve exposure to corrosive chemicals and extreme temperatures.
• 316 Stainless Steel: Contains molybdenum, which enhances its corrosion resistance, especially against chlorides and other industrial solvents. It is preferred for more corrosive environments, such as seawater and chemical processing.
• 316L Stainless Steel: A low-carbon variant of 316, it has reduced carbon content that minimizes carbide precipitation during welding, improving corrosion resistance in welded joints.

Applications

Stainless steel butterfly valves are chosen for their robust performance in various settings, including:

• Chemical Processing: For controlling the flow of aggressive chemicals, acids, and solvents.
• Food and Beverage Production: In systems requiring strict hygiene standards and resistance to food acids and cleaning agents.
• Pharmaceutical Manufacturing: Where cleanliness and contamination prevention are paramount.
• Water Treatment and Distribution: Suitable for handling both clean and wastewater, as well as desalination processes.
• Oil and Gas Industry: For applications requiring resistance to corrosion from saltwater, chemicals, and high-pressure conditions.

Selection Considerations

When selecting a stainless steel butterfly valve, it’s crucial to consider:

• Type of Fluid: Ensure compatibility with the fluid’s properties, including corrosiveness, temperature, and cleanliness requirements.
• Pressure and Temperature Ratings: Choose a valve that can withstand the system’s operating pressure and temperature range.
• Connection Type: Consider the valve’s connection type (wafer, lug, flanged) for compatibility with the piping system.
• Actuation Method: Determine whether manual, pneumatic, electric, or hydraulic actuation is best suited for the application’s operational needs.

In summary, stainless steel butterfly valves offer a reliable and efficient solution for flow control in a wide range of industrial applications. Their corrosion resistance, strength, and temperature tolerance make them a versatile choice for many fluid handling systems.

DUPLEX & SUPERDUPLEX STEEL

Butterfly valves made from duplex and super duplex stainless steels are engineered for applications requiring exceptional strength and corrosion resistance, especially in harsh and aggressive environments. Duplex stainless steels combine the properties of austenitic and ferritic stainless steels, resulting in materials that offer both high strength and excellent resistance to corrosion, including stress corrosion cracking. Super duplex stainless steels provide even higher corrosion resistance and strength, making them suitable for more demanding applications.

Characteristics of Duplex and Super Duplex Stainless Steel Butterfly Valves

• High Strength: Duplex and super duplex stainless steels have higher strength compared to austenitic stainless steels, allowing for the design of thinner valve bodies and components without compromising integrity.
• Superior Corrosion Resistance: These materials are highly resistant to a wide range of corrosive environments, including those containing chlorides, making them ideal for use in marine, chemical processing, and oil & gas applications.
• Good Fatigue Resistance: The combination of strength and corrosion resistance makes duplex and super duplex valves highly resistant to fatigue, extending their service life under cyclic loading conditions.
• Resistance to Stress Corrosion Cracking: Particularly in chloride-containing environments, duplex, and super duplex steels exhibit superior resistance to stress corrosion cracking, a common issue for standard austenitic stainless steels in certain conditions.

Common Grades

• Duplex Stainless Steel (UNS S31803, S32205): Features a balanced microstructure of austenite and ferrite, offering good resistance to pitting and crevice corrosion, high strength, and good weldability.
• Super Duplex Stainless Steel (UNS S32750, S32760): Contains higher levels of chromium, molybdenum, and nitrogen, providing even greater resistance to corrosion and increased strength compared to duplex stainless steel.

Applications

Butterfly valves constructed from duplex and super duplex stainless steels are particularly suited for:

• Offshore Oil and Gas Operations: In environments exposed to seawater, sour gas, and other corrosive substances.
• Chemical Processing: For handling aggressive chemicals, especially where chloride-induced corrosion is a concern.
• Desalination Plants: Where valves are exposed to highly corrosive seawater.
• Marine Applications: Including shipping and coastal facilities, where saltwater corrosion is an ongoing challenge.
• Pulp and Paper Industry: For processes involving corrosive chemicals used in paper production.

Selection Considerations

When choosing duplex or super duplex stainless steel butterfly valves, factors to consider include:

• Corrosion Resistance Needs: Assess the specific corrosive elements present in the application environment to select the most appropriate material grade.
• Pressure and Temperature Requirements: Ensure the selected valve can withstand the operating pressures and temperatures of the system.
• Cost-Effectiveness: While duplex and super duplex steels offer superior properties, they also come at a higher cost compared to standard stainless steels. Evaluate the long-term benefits of their use in reducing maintenance and replacement costs.
• Weldability and Fabrication: Consider the welding and fabrication requirements, as duplex and super duplex materials may require specific techniques and precautions during manufacturing and installation.

In summary, butterfly valves made from duplex and super duplex stainless steels provide a robust solution for controlling flow in environments where corrosion resistance and mechanical strength are critical. Their superior properties make them an excellent choice for demanding industrial applications where conventional stainless steels might not suffice.

NICKEL ALLOY STEEL

Butterfly valves made from nickel alloys are designed for the most demanding applications, offering exceptional resistance to corrosion, heat, and pressure. Nickel alloys, such as Inconel, Hastelloy, Monel, and Nickel 200/201, are renowned for their ability to withstand extreme environments, making them ideal for critical and high-performance applications across various industries.

Characteristics

• Corrosion Resistance: Nickel alloys provide excellent resistance to a wide range of corrosive environments, including seawater, chlorine, and acidic or alkaline substances. They are particularly effective against corrosion that challenges other materials, such as stress-corrosion cracking.
• High-Temperature Performance: These alloys maintain their strength and resistance even at very high temperatures, making them suitable for applications involving heat.
• Durability: The inherent strength and corrosion resistance of nickel alloys ensure that butterfly valves made from these materials have a long service life, even in harsh conditions.

Common Nickel Alloys Used for Butterfly Valves

• Inconel (e.g., Inconel 625, Inconel 718): Known for high strength and excellent corrosion resistance, especially in high-temperature environments.
• Hastelloy (e.g., Hastelloy C-276, Hastelloy C-22): Offers outstanding resistance to strong oxidizing agents and is used in severe corrosive environments.
• Monel (e.g., Monel 400, Monel K-500): Exhibits excellent resistance to seawater and caustic environments, combining good corrosion resistance with high strength.
• Nickel 200/201: Pure nickel or nearly pure nickel, providing excellent resistance to corrosion by alkaline substances and good thermal, electrical, and magnetostrictive properties.

Applications

Nickel alloy butterfly valves are used in situations where conventional materials would fail, including:

• Chemical Processing: For handling aggressive chemicals, solvents, and gases that require superior corrosion resistance.
• Oil and Gas Industry: Especially in sour gas applications where hydrogen sulfide can cause sulfide stress cracking in other materials.
• Power Generation: In applications involving high temperatures or corrosive gases.
• Marine and Offshore: For seawater systems and environments exposed to marine atmospheres, where corrosion resistance is critical.
• Pharmaceuticals: In processes requiring clean, non-contaminating materials.

Selection Considerations

When choosing nickel alloy butterfly valves, consider:

• Specific Corrosion Resistance Needs: Match the alloy to the particular corrosive agents present in the process or environment.
• Temperature Range: Ensure the chosen alloy can withstand the operational temperature extremes.
• Pressure Ratings: Verify that the valve can handle the system’s pressure requirements without compromising its integrity or performance.
• Cost-Effectiveness: Nickel alloys tend to be more expensive than other materials, so consider the long-term benefits of reduced maintenance and replacement costs against the initial investment.

Nickel alloy butterfly valves represent a high-end solution for controlling flow in applications where extreme conditions would compromise lesser materials. Their use can significantly enhance system reliability, safety, and longevity, albeit at a higher initial cost. The choice of a specific nickel alloy should be based on a thorough analysis of the application’s requirements, including exposure to corrosive substances, temperature, and pressure conditions.

TITANIUM AND TITANIUM ALLOYS

Butterfly valves made from titanium are renowned for their exceptional strength-to-weight ratio, outstanding corrosion resistance, and excellent durability under challenging conditions. Titanium and its alloys are lightweight yet offer mechanical properties comparable to those of some steel grades, making them an excellent choice for butterfly valves in specific applications.

Characteristics

• Corrosion Resistance: Titanium is exceptionally resistant to corrosion by seawater, chlorides, and many acidic environments, making it suitable for applications where other materials might fail.
• Strength and Durability: Despite being lightweight, titanium maintains high strength and withstands extreme pressures and temperatures, contributing to the longevity of the valve.
• Non-Magnetic and Biocompatible: Titanium is non-magnetic and biocompatible, expanding its use to applications where magnetic interference is a concern or where it contacts biological materials.
• Temperature Resistance: Titanium valves can operate effectively across a broad temperature range, maintaining their integrity in both low and high-temperature environments.

Applications

Titanium butterfly valves are ideal for industries and applications that demand material properties beyond what conventional metals can provide, including:

• Chemical Processing: For handling highly corrosive substances, such as chlorine and acids, where titanium’s corrosion resistance ensures reliability and safety.
• Seawater and Desalination: In seawater desalination plants, offshore platforms, and marine applications, where the resistance to seawater corrosion is critical.
• Pharmaceutical and Food Processing: Where the non-toxic and biocompatible nature of titanium is essential for avoiding contamination.
• Aerospace and High-Performance Engineering: In applications requiring materials that can withstand high temperatures and pressures without significant weight penalties.

Selection Considerations

When selecting titanium butterfly valves, consider the following factors:

• Grade of Titanium: Various grades of titanium offer different properties. For example, Grade 2 titanium is commercially pure and widely used for general corrosion resistance, while Grade 5 (Ti-6Al-4V) is an alloy known for its higher strength and used in more demanding applications.
• Cost: Titanium is more expensive than many other materials due to its processing complexity and raw material costs. Consider the long-term benefits of reduced maintenance and longer service life against the initial investment.
• Compatibility: Ensure the specific grade of titanium chosen is compatible with the fluid media, operating conditions, and environmental exposure of the application.
• Fabrication and Repair: Consider the availability of resources for fabrication and repair, as working with titanium requires specific expertise and equipment.

Titanium butterfly valves represent a high-end solution for controlling flow in demanding applications where conventional materials are inadequate. Their selection is justified in environments that require exceptional corrosion resistance, strength, and durability, despite their higher initial cost. The benefits of using titanium include extended equipment life, reduced maintenance, and improved safety and reliability in critical applications.

ALUMINIUM

• Properties: Lightweight, good corrosion resistance, and ease of machining.
• Applications: Primarily used in low-pressure applications, such as air handling, vacuum services, and dry bulk handling.

NICKEL ALUMINIUM BRONZE

This is a copper alloy that contains approximately 10% aluminum, 5% nickel, and 5% iron. It features strong corrosion resistance, especially in seawater applications, and resists the formation of a biofilm, a frequent cause of corrosion problems for stainless steels.

Butterfly valves API 609 may have soft or metal seats. Valves with soft seats are also called “soft-seated” or “resilient” butterfly valves and are of the centric type. Eccentric designs (double or triple offset) are available, generally, with metal seat designs, which could also be fireproof.

For less critical applications, butterfly valves are also available in plastic-grade materials, such as PVC, CVPC, Polypropylene (PP), and Polyethylene (PE). Here are the main features of plastic butterfly valves:

PVC

• Properties: Excellent corrosion resistance to a wide range of chemicals, lightweight, and cost-effective.
• Applications: Suitable for low-pressure applications, including water treatment, chemical processing, and irrigation systems.

CPVC

• Properties: Similar to PVC but can withstand higher temperatures.
• Applications: Used in hot water distribution, and chemical processing where higher temperature resistance than PVC is needed.

PP/PE

• Properties: Excellent chemical and corrosion resistance, lightweight, and suitable for a wide range of temperatures.
• Applications: Chemical processing, water treatment, and applications involving aggressive or corrosive fluids.

VALVE SEAT

SOFT SEATED BUTTERFLY VALVE (“RESILIENT”)

Soft-seated butterfly valves are designed to provide a tight seal and are typically used in applications where the sealing of gases or liquids is critical and where the operating conditions are within moderate temperature and pressure ranges. The “soft seat” refers to the use of elastomeric or other non-metallic, resilient materials for the sealing mechanism between the disc and the valve body, enhancing the valve’s ability to create a tight shut-off.

Key Features

• Sealing Material: The soft seat is usually made from materials such as PTFE (Polytetrafluoroethylene), NBR (Nitrile Butadiene Rubber), EPDM (Ethylene Propylene Diene Monomer), or Viton (a type of fluoroelastomer). Each material offers different properties in terms of chemical resistance, temperature tolerance, and wear characteristics, making them suitable for various applications.
• Tight Shut-Off: Soft-seated butterfly valves are known for their excellent sealing capabilities, providing a near bubble-tight closure. This makes them ideal for applications requiring precise control over the flow and leakage prevention.
• Low Torque Operation: The soft seating material reduces the friction between the disc and the seat, allowing for easy operation with minimal torque requirements.
• Application Versatility: These valves are used in a wide range of applications, from water and wastewater treatment to chemical processing, food and beverage, and HVAC systems, handling a variety of fluids, including corrosive and abrasive media.

Applications

Soft-seated butterfly valves are versatile and can be employed in various industrial and commercial applications, including:

• Water and Wastewater: For controlling and regulating water flow in treatment plants, distribution systems, and irrigation.
• Chemical Processing: Handling mild to moderately corrosive fluids, depending on the seat material’s chemical compatibility.
• Food and Beverage: In processes requiring sanitary conditions, where non-toxic and cleanable sealing materials like PTFE are essential.
• Air and Gas Handling: For applications involving air, natural gas, and other gases where a tight seal is crucial to prevent leakage.

Considerations

While soft-seated butterfly valves offer many advantages, there are considerations to keep in mind when selecting them for specific applications:

• Temperature Limits: The elastomeric and plastic materials used for the seats have upper temperature limits, beyond which they may degrade or lose their sealing properties.
• Chemical Compatibility: It’s essential to ensure that the seat material is compatible with the process fluid to prevent damage and ensure long-term reliability.
• Wear and Tear: While soft seats provide excellent sealing, they may be more prone to wear and damage from abrasive media than metal-seated valves.

In summary, soft-seated butterfly valves offer excellent sealing capabilities and are suitable for a wide range of applications requiring precise flow control and tight shut-off. Selecting the appropriate seat material based on the application’s specific requirements is crucial for optimal performance and longevity.

Soft seated butterfly valves (resilient) feature EPDM, VITON, NBR, BUNA-N, and similar soft seats. Soft-seat butterfly valves are generally of the concentric type and suit low-pressure and non-critical applications

METAL SEATED BUTTERFLY VALVE

Metal-seated butterfly valves are designed for more demanding applications where high temperatures, higher pressures, and abrasive or corrosive media are present. Unlike soft-seated valves, which use elastomeric materials for sealing, metal-seated valves rely on metal-to-metal contact between the disc and the seat, providing durability and resistance in harsh conditions.

Key Features

• Durability: Metal seats are highly durable and resistant to wear, making them suitable for applications involving abrasive particles or high-velocity flows that could damage softer seat materials.
• High Temperature and Pressure Resistance: Metal-seated butterfly valves can withstand higher temperatures and pressures than their soft-seated counterparts, making them ideal for industrial processes involving steam, hot gases, or high-pressure fluids.
• Corrosion Resistance: Depending on the metals used (such as stainless steel, Hastelloy, Inconel, or others), these valves offer excellent resistance to corrosion and chemical attack.
• Leakage: Metal-seated valves may not provide the same level of tight shut-off as soft-seated valves. They are generally designed to meet industry standards for acceptable leakage rates under specific conditions, which is often sufficient for many high-temperature and high-pressure applications.

Materials for Metal Seats

Applications

Metal-seated butterfly valves are chosen for their robustness in challenging environments, including:

• Power Generation: For handling steam and high-temperature water in cooling systems and boilers.
• Chemical and Petrochemical Industries: In processes involving corrosive fluids, high temperatures, and where valve durability is crucial.
• Mining and Minerals Processing: For slurry and abrasive material handling where valve wear is a concern.
• Pulp and Paper Manufacturing: In applications involving high-temperature liquids and corrosive chemicals used in the pulping process.

Considerations

When selecting a metal-seated butterfly valve, several factors should be considered to ensure it meets the application’s needs:

• Sealing Requirements: While metal-seated valves are durable and handle extreme conditions, they might not achieve the absolute tight shut-off possible with soft-seated valves. Consider the application’s leakage tolerance.
• Material Compatibility: Choose a valve body and seat material that is compatible with the process media and conditions to ensure long-term reliability and performance.
• Operational Torque: Metal-to-metal seating can require higher torque to operate the valve, impacting actuator selection and operational energy costs.
• Cost: Metal-seated valves, especially those made from exotic alloys for enhanced corrosion resistance, can be more expensive than soft-seated valves. However, their durability in harsh conditions may offer a lower total cost of ownership over time.

In summary, metal-seated butterfly valves are an excellent choice for industrial applications that demand high durability, temperature resistance, and the ability to handle abrasive or corrosive media. Proper selection of valve materials and understanding the specific operational requirements are key to maximizing the performance and lifespan of these valves in demanding environments.