What are Butterfly Valves? How They Work & Types: an Overview

1. What is a Butterfly Valve? What are the Working Principles of Butterfly Valves?

 

A butterfly valve is a quarter-turn rotational device in piping systems that controls fluid flow via a disc rotated by an external mechanism. When the disc coplanar with flow, it fully obstructs; otherwise, it permits partial or complete flow. It takes a 90° turn to fully open, with the disc vertical to flow. This valve regulates flow within large pipe diameters by quarter-turn rotation of a disc, altering pressure for any position. It's called a butterfly valve because it moves like a butterfly's wings. It's like when a butterfly lands and its wings flap up and down in a 90-degree motion.

 

2. Parts of a Butterfly Valve

The primary elements of a butterfly valve include the body, stem, disc, and seat. The designs of each component varybased on the materials, the type of flow media, the intended purpose, etc.

 

 

2.1 Body

The primary structure of the valve provides the central flow passageway and connection points to the piping. It's typically made of robust materials like cast iron, stainless steel, or engineered plastics to withstand the pressures and fluids it will handle. Body styles play a role in how the valve is installed.

 

2.2 Disc

The heart of the valve is the disc, which rotates to control flow. It is made of various materials, such as metals or polymers, and may be solid or have holes to reduce weight. Concentric and eccentric disc options are most common.

 

2.3 Stem

The butterfly valve's stem may seem small, but it's crucial. It links the inside disk to the outside handle, enabling the valve to open or close. Without it, the valve would be useless. The stem comes in two designs—wetted and non-wetted—referring to its protection. Non-wetted stems are shielded from corrosive or erosive substances in the line, while wetted stems are not, requiring materials compatible with the flowing media.

 

2.4 Seat

This is the sealing surface within the valve body where the disc rests when closed. Seats are crucial for a tight seal and are usually made from softer materials like elastomers, PTFE, or similar polymers for leak prevention. Common materials are:

 

• Resilient seat: Entirely made of a soft material, providing excellent sealing but potentially more vulnerable to wear from abrasive fluids.
• Metal seat: This is a very durable design for extreme conditions, but the sealing may not be as perfect as that of a resilient seat.
• Hybrid seats: Combine elements of both designs for a balance of properties

 

3. Advantages of Butterfly Valves

3.1 Compact and lightweight

Butterfly valves boast a space-saving, streamlined design and use less material in their construction. This makes them significantly lighter than comparable gate or globe valves, simplifying installation and making them ideal for applications with tight space restrictions.

 

3.2 Cost-effective

Butterfly valves' simple design and lower material requirements typically translate to lower manufacturing costs compared to other valve types. This cost advantage extends to installation, as their lighter weight and compact design can reduce labor and material needs.

 

3.3 Low-pressure drop

When fully open, the disc of a butterfly valve sits mainly parallel to the flow path, presenting minimal obstruction. This results in minimal pressure loss for the fluid passing through, potentially reducing energy costs in pumping systems.

 

3.4 Quick operation

Butterfly valves' quarter-turn operation allows them to quickly change from fully open to fully closed. This makes them invaluable when rapid shutoff is needed or processes require frequent flow adjustments.

 

4. Disadvantages of Butterfly Valves

4.1 Limited throttling capabilities

The traditional disc design of a butterfly valve isn't ideal for precise flow control, especially at low rates, as the position of the disc can lead to turbulent flow. However, specialized butterfly valves with eccentric disc shapes can improve fine flow control.
 

4.2 Potential for disc wear

Systems with high pressures or abrasive fluids flowing through the valve can accelerate wear on the seat. Material selection and regular maintenance become important factors in the valve's long-term performance in such conditions.

 

5. Types of Butterfly Valves

Butterfly valves come in several variations, classified primarily by their body connection method and disc closure design:

 

5.1 Body Connection Design

 

Wafer-style

The wafer design is most cost-effective variant of the butterfly valve. The wafer type is positioned between two pipe flanges, secured by flange bolts encircling the valve body. Long bolts pass through the entire valve body, connecting the pipe flanges. Sealing between the valve and pipe flanges is achieved using a snugly fitted seal, like an O-ring or gasket, along with a flat valve face on the downstream and upstream sections. This connection design ensures sealing against bi-directional differential pressures and prevents backward flow in systems intended for universal flow.

 

 

 

Lugged-style

The lug-type butterfly valve features threaded lugs positioned on the exterior of the valve body. Pipe flanges are connected to each side of the bolt inserts using two sets of bolts, eliminating the need for nuts. This setup allows one side to disconnect without impacting the other, which is particularly useful for dead-end service applications. Unlike wafer-style valves, lug-type butterfly valves bear the weight of the piping through the valve body.

 

 

5.2 Disc Closure Design

The disc closure design significantly influences butterfly valve performance. Understanding the options is critical to selecting the suitable valve for a specific application:

 

Concentric 

The most common type has a stem running through the centerline of the disk. It is frequently utilized in low-pressure situations.

 

Eccentric

This design features a stem that doesn't go through the center line but instead goes behind it, opposite the flow. It was created to prevent the disk and seal from touching too soon before fully closing, reducing operational torque and minimizing valve wear. Hence, the design significantly prolongs the valve's lifespan.

 

In a double offset or doubly eccentric butterfly valve, the stem is positioned behind the disc’s centerline with an extra offset to one side. This double eccentricity design minimizes contact between the disc and seat, occurring only in the final 1-3° disc closure. 

 

 

 

On the other hand, a triple offset butterfly valve (TOV or TOBV), designed for critical applications, shares a similar structure with the double offset valve but incorporates a third offset, which is the axis of disc-seat contact. The seat surface and the ridge of the disc both have a conical shape, ensuring minimal contact before full valve closure. Triple offset butterfly valves are more efficient and endure less wear, often featuring metal seats for a tight seal, making them suitable for higher temperature ranges.

 

STREAMING provides various types of butterfly valves for every special needs. Check out STREAMING wafer-style, lugged-style, and eccentric butterfly valves.

 

6. Materials for the Construction of Butterfly Valves

The valve body requires robust 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. Metal and plastic are the main materials utilized in the butterfly valves.

 

6.1 Metals: Stainless steel

Stainless steel is an alloy with elevated chromium content (10.5-30%) and trace amounts of nickel and molybdenum, which boasts exceptional strength, toughness, and resistance to corrosion and weathering. Its corrosion resistance is primarily due to forming a thin, protective chromium oxide layer, which prevents oxygen diffusion into the material's bulk. This layer can reform in case of surface damage, rendering stainless steel self-healing against rust. Additionally, molybdenum contributes to its resistance to pitting corrosion. Thanks to this robust material, stainless steel butterfly valves excel in handling acidic and corrosive fluids across a broad spectrum of pressures and temperatures. 

 

6.2 Metals: Carbon steel

Carbon steel has a higher carbon content of up to 2.5%. Commonly employed grades for butterfly valves include ASTM A216 WCB (Welded Cast B-grade) and LCC (Low Carbon Content), with WCB suitable for high-temperature environments and LCC for low-temperature conditions. While carbon steel butterfly valves present a cost-effective alternative to stainless steel counterparts, they are not suitable for handling corrosive fluids due to their susceptibility to corrosion.

 

6.3 Metals: Cast Iron

Cast iron, a ferrous alloy primarily composed of iron, carbon, and silicon, is renowned for its strength, longevity, and heat resistance. Its robustness and resistance to deformation make it ideal for applications subjected to high temperatures and heavy loads. Cast iron butterfly valves, utilizing these features, are commonly employed in water purification, wastewater treatment, food processing, and pharmaceutical manufacturing. However, cast iron is susceptible to corrosion in highly acidic or alkaline environments, which can lead to deterioration over time. Therefore, it is essential to assess the compatibility of cast iron with the specific operating conditions before implementation.

 

6.4 Metals: Hastelloy

Hastelloy, an alloy comprising nickel, chromium, and molybdenum, was pioneered by Haynes International, Inc. Renowned for its robustness, it maintains high strength even at elevated temperatures. It exhibits exceptional resistance against corrosion, cracking, and oxidizing and reducing agents. Hastelloy butterfly valves are prevalent in industries such as oil and gas processing and power generation, and they are particularly suitable for handling nitric, hydrochloric, and sulfuric acids under moderate temperatures.

 

6.5 Plastics: PTFE for Soft Seats

Polytetrafluoroethylene (PTFE), commonly called Teflon, is the preferred material for valve seats due to its synthetic fluoropolymer composition. Renowned for its low friction, high resilience, and exceptional chemical and fire resistance, PTFE finds extensive use in various industries, including food and pharmaceutical manufacturing, thanks to its non-toxic properties. Operating seamlessly within a temperature range of -100°F to 450°F, PTFE seats ensure reliable performance across diverse applications.

 

6.6 Plastics: EPDM for Soft Seats

Ethylene-propylene diene monomer (EPDM) is a synthetic rubber known for its toughness and resistance to wear and tear. EPDM valve seats are versatile and capable of handling acids, alcohols, and alkaline solutions, making them ideal for applications like chlorinated water treatment and handling sulfuric acid. EPDM is also ozone-resistant, but it's important to note its incompatibility with petroleum-based products and turpentine. EPDM seats operate effectively within a temperature range of -20°F to 230°F, ensuring reliable performance across various industries and environments.

 

7. Common Butterfly Valve Uses

7.1 Water & Wastewater Treatment

Butterfly valves are ideal for handling large volumes of water, slurries, and sludge due to their minimal flow obstruction and cost-effectiveness in large sizes. Their simple operation also makes them easy to manage within complex treatment systems.

 

7.2 HVAC

Large-diameter butterfly valves offer efficient airflow control in heating, ventilation, and air conditioning systems. Their lightweight and space-saving design simplifies installation within building ductwork.

 

7.3 Chemical Processing

The wide range of materials, such as stainless steels, plastics, and specialty alloys, and seat options allows butterfly valves to be tailored to specific chemicals and corrosive environments. Their quarter-turn operation is also beneficial in processes where fast adjustments are needed.

 

7.4 Oil and Gas

Butterfly valves find use throughout the oil and gas industry due to their ability to handle large volumes of fluids and their availability in high-pressure configurations. Robust materials options meet the demands of both exploration and refining operations.

 

7.5 Power Generation

Butterfly valves effectively control cooling water, steam, and other process fluids in power plants. Specialized high-performance butterfly valves with suitable seals and materials can withstand the high temperatures commonly found in power generation.

 

7.6 Pulp and Paper

Butterfly valves effectively handle the paper pulp, slurries, and chemicals involved in paper production processes. Materials are carefully chosen to resist abrasion and the specific chemicals used in pulping.

 

STREAMING - Your Best Butterfly Valve Supplier

If you're looking for high-quality butterfly valves for your industrial needs, look no further than STREAMING. Here's why:

 

• Unmatched Quality: Our valves are built to last, delivering dependable performance in even the most demanding applications.
• Comprehensive Selection: Find the perfect valve for your system with our vast range of designs, materials, and sizes.
• Expert Support: Our team is ready to guide you through the selection process, ensuring you get the optimal solution for your unique requirements.

 

Our commitment to quality, extensive product range, and expertise make us a trusted partner. STREAMING has the right solution for your application with various butterfly valve designs, materials, and sizes. 

 

Contact us today to learn more and let us help you find the perfect butterfly valves to streamline your operations.

 

FAQs

What is a butterfly valve used for?

Butterfly valves are versatile flow control devices used in various industries to regulate the flow of liquids, gasses, and slurries. They are commonly found in water treatment, HVAC, chemical processing, oil and gas, and many other applications.

 

What is the problem with the butterfly valve?

Butterfly valves have two main drawbacks: restricted throttling, making them less than ideal for precise flow control, especially at low flow rates, and susceptibility to wear. Another is susceptibility to wear because high pressure or abrasive conditions can lead to disc wear, potentially compromising sealing effectiveness.

 

Which is better: butterfly valve or ball valve?

The best choice depends on your needs. 

Our Ball valves offer superior tight shutoff and are better for precise flow control.

Our Butterfly valves are generally more cost-effective and have a smaller footprint.