This article takes a detailed look at butterfly valves.
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A butterfly valve is a type of quarter-turn rotary control mechanism used to regulate the flow of fluids in a pipeline system. Its operation is based on a rotating disc situated directly within the flow route. This disc is maneuvered by an external actuator, which is linked via a stem. When the disc aligns itself parallel with the flow, it fully obstructs fluid passage. Conversely, when it is set perpendicularly, the fluid can freely flow through. A 90-degree rotation of the disc is needed to open or seal the valve.
Similar to ball valves and plug valves, butterfly valves are quarter-turn valves. These devices exhibit a straightforward construction and operational principle and are designed compactly to fit between two pipe flanges. They can be manually operated or automated using an actuation system incorporated into the pipeline's process control. While ideal for simple on-off applications, their functionality for controlling flow throttling is somewhat restricted.
Available in a wide array of models and configurations, butterfly valves are built to sustain different temperature ranges, pressures, and flow volumes. Each valve type is precisely engineered to meet the unique needs of pipeline systems managing both liquid and gaseous flows.
The primary components of a butterfly valve include the following:
When the disc is perpendicular to the flow’s cross-sectional area, fluid is fully obstructed from passing through the valve. Conversely, rotating the disc allows fluid to flow through the space between the seat and the disc. A 90° rotation from the closed position enables full opening or closing of the valve, while positioning the disc at intermediate angles provides effective throttling and regulation of flow. Because of its efficient design, the butterfly valve disc is often compared to the ball in ball valves or a plug in plug valves, and is commonly used in isolation and control processes across industries.
Butterfly valve seats can be categorized as soft seats or metal seats. Soft seats—made from elastomeric or thermoplastic materials like EPDM, PTFE, or NBR—are often used for lower temperature and pressure applications, providing bubble-tight shutoff. Metal seats, typically constructed from stainless steel or other alloys, are designed for high-temperature, high-pressure, or abrasive service, offering extended service life though sometimes at the expense of minimal leakage. The selection of seat material directly impacts the temperature, pressure, and chemical compatibility of the butterfly valve.
Manual operation involves applying torque to the lever or handwheel connected to the stem, setting the valve in fully-closed, fully-open, or partially-open positions for regulating media. Larger butterfly valves or those requiring frequent operation are equipped with gear operators or chain wheel mechanisms to increase torque and facilitate easier valve operation. For high-cycle or remotely located installations, butterfly valves employ actuators—these may be electric (electromechanical), pneumatic (using compressed air to move a piston or diaphragm), or hydraulic (operated by fluid pressure). Advanced actuation also supports networked process control in industrial automation and building management systems, increasing efficiency and reducing requirements for manual intervention.
Additional Key Features
When selecting, specifying, or replacing a butterfly valve, consider not just its internal components, but also materials of construction, performance requirements, end connection types, and compliance with relevant standards. These factors will help ensure optimal performance, longevity, and suitability for your industrial or commercial fluid handling application.
Butterfly valves are versatile flow control devices engineered to provide effective and dependable shut-off and throttling in industrial piping systems. These quarter-turn valves are chosen for their compact design, low pressure drop, and rapid operation. Butterfly valves come in two primary designs: centric (concentric) and eccentric. Centric butterfly valves have the stem positioned centrally through the valve disc, while eccentric butterfly valves feature one or more stem offsets, separated from the disc’s centerline for specialized performance. Eccentric valves are further divided by the number of offsets—single, double, or triple offset configurations—offering enhanced sealing, reduced friction, and higher durability, making butterfly valves highly desirable in process control, water treatment, oil & gas, chemical, HVAC, and power generation sectors.
Zero offset butterfly valves, also known as concentric butterfly valves, feature a stem that runs through the centerline of the disc, precisely centered within the resilient seat and the valve body. When closed, all elements align concentrically. The disc can rotate a full 360°, and in its open position, fluid flow is divided efficiently on either side. A key advantage is that the flowing media does not contact the metal valve body, as the seat material, typically rubber or elastomer, provides a protective barrier.
These valves utilize resilient soft seats, relying on seat deformation for tight shut-off and leak-free sealing. However, the sliding action of the disc against the seat creates friction, potentially reducing cycle life under frequent use. Common materials for the seat include EPDM, NBR, and PTFE, making zero offset butterfly valves well-suited for low to medium pressure applications (up to 250 psi) and moderate temperature ranges (up to 400°F). This makes them ideal for potable water, air, non-corrosive gases, and basic chemical services as cost-effective isolation or regulation valves.
Double offset butterfly valves, often referred to as high-performance butterfly valves, are engineered with two distinct stem offsets relative to the seat centerline and body centerline. The first offset positions the stem behind the seat axis, while the second moves the stem off from the pipe’s vertical axis. This configuration “lifts� the seat from the disc during the opening and closing movements, drastically reducing friction and wear—especially around the first and last 10 degrees of movement.
Double offset butterfly valves typically feature a soft seat with a metal backing for enhanced performance at higher pressures and temperatures than zero offset models. Their robust construction makes them suitable for demanding liquid and gas applications, including water treatment plants, chemical process lines, HVAC systems, fire protection, and industrial utilities. They are recognized for delivering improved tightness, extended cycle life, and reliable performance in systems where standard resilient-seated valves may not suffice.
Triple offset butterfly valves add a third, angular offset to the body’s sealing cone axis in addition to the initial two offsets, producing a right-angled, conical seating geometry. With this design, the seat and disc only contact each other momentarily at the closed position, virtually eliminating friction during operation. This allows for precise shut-off and exceptional durability under severe operating conditions.
Constructed with robust metal seats—often in stainless steel or alloy—the triple offset butterfly valve excels in applications demanding tight shut-off at high pressures and high temperatures. This configuration is ideal for managing superheated steam, high-temperature liquids, aggressive chemicals, and challenging gases found in power generation, oil and gas processing, petrochemical operations, pulp and paper manufacturing, and offshore pipelines. Metal-seated triple offset valves are also fire-safe and suitable for critical process control where zero leakage is essential.
In addition to superior sealing and high cycle life, triple offset butterfly valves demonstrate outstanding resistance to thermal and mechanical shock, extreme pressure fluctuations, and corrosive environments. Their unique construction makes them the preferred choice in safety-critical and severe service applications requiring reliable isolation.
Butterfly valves can also be categorized according to their connection type and installation method within a piping system:
Wafer butterfly valves are slim-profile valves that are installed between two pipe flanges. Long through-bolts traverse the valve body, which may have, or lack, external flange holes. To prevent backflow and leakage, O-rings or flat face gaskets are compressed on both sides of the valve body, creating a tight seal. Wafer-style butterfly valves are a popular, cost-effective choice for systems requiring light weight, easy installation, and a lower investment cost.
While wafer butterfly valves provide excellent, compact shut-off for liquids and gases, they are not recommended for dead-end (end-of-line) service as they cannot withstand unbalanced pressure when one side is removed. Pipeline maintenance or component replacement normally necessitates full shutdown of the system. This style is generally suitable for moderate pressure and temperature systems and is not ideal for high-temperature, steam, or harsh chemical services that may cause thermal expansion or seat degradation.
Lug butterfly valves install between two pipe flanges using threaded mounting lugs protruding from the valve body. Specialized bolts connect each side directly, and unlike wafer butterfly valves, lug valves permit disconnection of one pipeline segment without disturbing the other side. This “dead-end service� capability makes them versatile for on-line maintenance and point-of-isolation requirements.
Lug-style valves must withstand added load, as the valve body supports the pipeline segment when used in end-of-line service. This increases engineering considerations for seat integrity and permissible pressure ratings. They are frequently used in water distribution, process isolation, and industrial plant piping where system flexibility and streamlined repairs are required.
Double-flanged butterfly valves feature flange connections on both sides of the valve body, precisely matching pipe flanges with dedicated bolts and nuts for secure, vibration-resistant installation. This robust mounting arrangement provides optimal strength, alignment, and leak prevention—especially for large-diameter pipelines and critical systems subject to frequent operation, surges, or high pressures. Municipal water, wastewater treatment, and major process lines often utilize double-flanged valves due to their stability and operator safety.
Butt-weld butterfly valves are welded directly into the pipeline, creating a permanent, pressure-tight joint ideal for severe service, high-pressure, or high-temperature environments. Their seamless integration minimizes potential leak paths and withstands pipe stresses, making them the preferred solution in power plants, oil and gas transmission networks, chemical manufacturing, and applications with strict leakage or fire safety codes. Butt-welded butterfly valves offer enhanced mechanical strength and reduced maintenance.
Top entry butterfly valves are engineered for simplified maintenance and minimal downtime. Their unique construction enables the removal of the bonnet, providing direct access to the stem, disc, and seat from above. This design eliminates the need for full pipeline disassembly when replacing internal parts, allowing cost-effective valve repair, part replacement, or inspection in-line. Top entry designs are especially advantageous in critical process or hazardous service environments where continuous uptime is paramount.
Butterfly valves are also classified as “non-wetted� or “wetted� valves according to their construction and degree of exposure of internal surfaces to the operating media:
In summary, understanding the types of butterfly valves—including seat design (resilient seat, high-performance or triple offset), installation method (wafer, lug, flanged, butt-weld, top entry), and material options (wetted or non-wetted)—is fundamental for selecting the right valve for your flow control needs. When evaluating butterfly valve products, consider the process fluid’s pressure, temperature, media composition, desired shut-off tightness, ease of maintenance, and compliance with relevant industry standards (such as API, ASME, or ISO). Advanced butterfly valve automation options, including pneumatic or electric actuators, can further optimize system performance and reliability for complex piping infrastructures.
The valve body needs to have high toughness and rigidity to safeguard the internal components of the butterfly valve. Similarly, the stem and disc must exhibit these qualities to endure fluid pressures. Butterfly valve components can be constructed from the following materials:
Stainless steel is an alloy with a high chromium content (10.5-30%) and small amounts of nickel and molybdenum. It is renowned for its exceptional strength, toughness, and resistance to corrosion and weathering. The corrosion resistance is primarily due to the chromium, which forms a thin, protective chromium oxide layer that prevents oxygen from penetrating the material. If the surface is damaged, this layer can regenerate with the help of oxygen, thus preventing rust. Molybdenum contributes to resistance against pitting corrosion.
Stainless steel butterfly valves are excellent for handling acidic and corrosive fluids, a wide range of pressures, and a wide range of temperatures. Austenitic stainless steel is ideal for cryogenic processes, while duplex stainless steel is used for higher pressure. 316 Stainless Steel is the preferred stainless-steel grade.
Carbon steel is an alloy with a carbon content of up to 2.5%. It offers good mechanical properties and is suitable for applications that do not have specialized requirements. Common grades of carbon steel used for butterfly valves include ASTM A216 WCB (Welded Cast B-grade) and LCC (Low Carbon Content). The WCB grade is suited for high-temperature applications, while the LCC grade is appropriate for low-temperature environments. These valves are typically produced using a sand-casting process for both the body and the disc.
While carbon steel butterfly valves are more cost-effective compared to their stainless steel counterparts, they are not suitable for handling corrosive fluids.
Hastelloy is an alloy made of nickel, chromium, and molybdenum, and was the first alloy developed by Haynes International, Inc. It is known for its high strength at elevated temperatures and its excellent resistance to corrosion, cracking, and both oxidizing and reducing agents. Hastelloy is suitable for handling acids such as nitric, hydrochloric, and sulfuric at moderate temperatures.
Hastelloy butterfly valves are commonly used in applications involving high temperatures, high pressures, and corrosive environments, including those found in oil and gas processing and power generation.
Brass is an alloy composed of copper and zinc, known for its toughness, durability, and ability to withstand high temperatures. It is prized for its resistance to corrosion and biofouling, as well as its antimicrobial properties, which help prevent the growth of microbes and biofilms on its surface.
Brass butterfly valves are commonly used in applications such as water purification, wastewater treatment, and in the food and pharmaceutical industries. However, they are not suitable for handling water with high chlorine content, such as seawater or swimming pool water, due to the risk of dezincification caused by chlorine.
Nickel alloys are renowned for their excellent resistance to corrosion, harsh environments, and high temperatures. They typically outperform stainless steel in extremely corrosive conditions. However, nickel butterfly valves tend to have a higher density and come at a greater cost.
Titanium alloys offer a high strength-to-weight ratio and are well-regarded for their resistance to corrosion and biofouling. They are suitable for use in seawater environments and water treatment applications due to their non-toxic nature. Despite these advantages, titanium butterfly valves are also quite expensive.
Nickel Aluminum Bronze is a copper-based alloy that includes 10% aluminum, 5% nickel, and 5% iron. This alloy is notable for its resistance to corrosion, antimicrobial properties, and ability to prevent biofouling. Nickel Aluminum Bronze butterfly valves are commonly used in seawater environments, such as offshore piping, as well as in water purification and wastewater treatment applications.
Butterfly valves can also be constructed from rigid plastic materials. Typically, plastic butterfly valves are lighter and more cost-effective than their metal counterparts. However, plastic materials have lower melting points, which restricts their maximum operating temperature.
PVC is a strong and rigid material commonly used in pipes, fittings, and valves. PVC butterfly valves are known for their durability and resistance to corrosion. They are suitable for handling most chemicals, although they should not be used with hydrocarbons or aromatic compounds. PVC valves are hygienic, easy to clean, and simple to assemble, making them ideal for applications in food and beverage processing. They are also used in water supply distribution, irrigation, plumbing, and water and wastewater treatment. PVC butterfly valves have a maximum operating temperature of 60°C and a pressure rating of 150 psi.
CPVC contains more chlorine than PVC and is produced through the free radical chlorination of PVC. This modification allows CPVC to handle higher temperatures, up to 93.3°C, and enhances its flexibility. However, CPVC is generally more expensive than PVC. CPVC butterfly valves are commonly used in both cold and hot potable water systems, industrial liquid handling, swimming pools, fountains, and other applications.
PP (Polypropylene) butterfly valves are known for their exceptional strength and durability in harsh environments. They resist corrosion, biofouling, and UV degradation, making them suitable for handling a wide range of chemicals and corrosive agents. However, they have selective compatibility with certain organic substances and solvents. PP butterfly valves are commonly used in aquaculture, water and wastewater treatment, and chemical manufacturing. They have a maximum operating temperature of 80°C.
GFPP (Glass-Filled Polypropylene) is an advanced modification of PP that incorporates glass fibers to enhance its rigidity, tensile strength, flexural strength, and dimensional stability. Similar to standard PP valves, GFPP butterfly valves are resistant to chemicals and corrosion. They are designed for more demanding environments and heavy-duty applications.
PVDF (Polyvinylidene Fluoride) butterfly valves are lightweight and offer exceptional corrosion resistance. They are highly abrasion-resistant, making them suitable for handling media with suspended solids. PVDF valves are ideal for high-purity applications and are compatible with most chemicals, including alcohols, hydrocarbons, and halogenated solvents, which makes them commonly used in chemical manufacturing. They also provide reliable, leak-free handling of substances. The maximum operating temperature for PVDF butterfly valves is 120°C.
ABS (Acrylonitrile Butadiene Styrene) is a thermoplastic polymer known for its strength, rigidity, and impact resistance. It is commonly used for constructing valve discs and is compatible with housings made from GFPP, PP, and PVC. ABS is relatively cost-effective. The maximum operating temperature for ABS is 60°C.
Butterfly valve seats are classified into two main types: soft seats and metal seats. The temperature ratings of butterfly valves are determined by the material used for the seat.
Soft seats are crafted from plastic or elastomeric materials known for their low friction and self-lubricating properties. While they typically have lower temperature and pressure ratings compared to metal seats, they are also more cost-effective.
Polytetrafluoroethylene (PTFE), commonly known as Teflon, is a synthetic fluoropolymer distinguished by its low friction, high durability, and exceptional resistance to chemicals and heat. Its non-toxic properties make it ideal for applications in the food and pharmaceutical sectors. PTFE valve seats operate efficiently in temperatures ranging from -100°F to 450°F.
Reinforced Polytetrafluoroethylene (RTFE) is an advanced form of PTFE that includes 15% glass fiber. This reinforcement enhances the wear resistance and compressive strength of the material. However, RTFE is not suitable for use with hydrofluoric acid or caustic soda due to its reaction with glass. RTFE seats are effective within a temperature range of -320°F to 450°F.
Ethylene-Propylene Diene Monomer (EPDM) is a synthetic rubber known for its exceptional elasticity and resistance to abrasion. EPDM valve seats are well-suited for handling acids, alcohols, and alkaline solutions, as well as chlorinated water, bleach, and concentrated sulfuric acid. It is also resistant to ozone, though it should not be used with petroleum-based solvents and oils. EPDM seats are rated for temperatures between -20°F and 230°F.
Buna-N, or nitrile rubber, is a versatile rubber with high durability and resistance to wear. Buna-N seats are effective for gases, water, fuels, petroleum, and alcohol. However, they are not suitable for use with acetones, ketones, chlorinated hydrocarbons, nitro hydrocarbons, or ozone. Buna-N seats operate within a temperature range of -35°F to 250°F.
Viton, also known as FKM, is a fluorocarbon elastomer compatible with a wide range of chemicals but is less effective for steam and water applications. Viton seats function well within temperatures from -20°F to 400°F.
Neoprene, or chloroprene rubber, is a synthetic rubber with good flexibility and resistance to greases, oils, fats, and most chemicals, except for strong oxidizers. It is flame-resistant and used in handling refrigerants and in pulp and paper manufacturing. Neoprene’s black color makes it less suitable for utility water in bleached paper production. Neoprene seats operate between -35°F and 225°F.
Metal seats are preferred for high-temperature applications as they retain strength and rigidity even at elevated temperatures. They also support higher pressure ratings due to their robust nature compared to soft seats.
Inconel, a nickel-chromium-molybdenum alloy, is known for its superior mechanical properties and resistance to corrosion, oxidation, and scaling in extreme conditions. Inconel seats can handle temperatures up to 90°F, with grades such as Inconel 625 and 600 being commonly used in metal seat construction.
Stainless steel is also an effective material for metal seats, offering a more cost-effective alternative to Inconel while still providing strong performance.
Stellite is a corrosion-resistant, non-magnetic cobalt-based alloy that includes chromium and tungsten. This alloy can be customized to suit different application requirements. Incorporating Stellite into valve seats has markedly enhanced their strength and longevity, providing substantial improvements in durability and performance.
Nitriding is a heat treatment technique designed to harden metal surfaces through the diffusion of nitrogen. This process is commonly employed for manufacturing valve seats and can be applied to materials such as low alloy steels, aluminum, molybdenum, and titanium. The nitriding process, which typically lasts several hours, enhances hardness, wear resistance, corrosion resistance, and high-temperature performance.
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