When To Use a Butterfly Valve

Figure 1: Butterfly valve for a cooling tower

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A butterfly valve is suitable for low to medium-pressure and variable-flow applications. It is a standard valve for large-diameter pipes that require compact and lightweight valves. Butterfly valves are frequently employed in water distribution, chemical processing, low-pressure applications, and more. They are suitable for throttling and fully open or closed applications, providing efficient flow control and regulation across multiple settings.

A butterfly valve controls fluid flow using a rotating disc attached to a central stem. In the closed position, the disc is perpendicular to the flow, blocking it. Rotating the stem 90 degrees aligns the disc parallel to the flow, allowing passage. The valve can also be partially opened to regulate flow. An o-ring prevents leakage along the stem. Read our butterfly valve overview article for more information on the design and various types of butterfly valves.

Table of contents

• When to use a butterfly valve
• Where are butterfly valves used
• Disadvantages
• Butterfly valves vs ball valves, gate valves, and globe valves
• FAQs

When to use a butterfly valve

A butterfly valve is an excellent choice in various applications due to multiple factors:

• Quick shutoff: Butterfly valves are ideal for rapid opening and closing, making them perfect for emergency shutdowns and fire suppression systems where quick isolation is crucial.
• Limited space requirement: Butterfly valves have a compact and streamlined design, requiring less space for installation than gate valves or globe valves, which is advantageous in tight spaces or where piping systems are congested. They are also cost-effective compared to other valve types.
• Applications involving large pipe sizes: When fully opened, the butterfly valve provides low flow resistance and precise flow control, making it commonly used for regulating large-diameter systems.
• Coarse media: Butterfly valves, depending on the strength of the seal, are suitable for handling media with suspended solid particles, powders, and granules. They are also effective for transporting mud or slurries, minimizing liquid accumulation at the pipe mouth.
• Limited torque requirements: Butterfly valves require less torque due to their quarter-turn operation, allowing for more miniature, more cost-effective actuators than other valves like gate valves.
• Flow regulation: While not as precise as globe valves, butterfly valves can be used for flow regulation and throttling, providing a good balance between flow control and pressure drop.
• Excellent mechanical properties: The valve rod in a butterfly valve is designed as a through rod structure. After tempering, it offers excellent mechanical properties, corrosion resistance, and scratch resistance. During operation, the valve rod rotates without lifting, reducing wear on the packing and ensuring reliable sealing.

Figure 2: Parts of a butterfly valve: disk (A), stem (B), handle (C), seal (D), o-ring (E), valve body (F)

Where are butterfly valves used

• Chemical industry: Used for on/off and modulating control of chemicals and liquids in processing and transportation.
• Oil and gas industry: Employed for isolation and regulation in pipelines and vessels.
• Water treatment: Utilized to control the flow of water and treatment chemicals, particularly in seawater and raw water management.
• HVAC systems: Essential for controlling flow rates and regulating air and fluid flow. Typically used in large duct systems to manage airflow, in chilled water systems to prevent cooling water flow, and in heating systems to regulate hot water flow.
• Food and beverage processing: Used to manage fluid flow during processing, ensuring sanitary conditions.
• Potable water: Water distribution systems are ideal for handling large fluid flows in pumping stations, water collection, transmission, and drinking water distribution and serve as flow isolation devices.

Disadvantages

• Limitations for high-pressure and high-temperature systems: Butterfly valves are generally unsuitable for very high-pressure/temperature applications, as they may be prone to leakage due to the design of the disc and seal.
  • Exception:  High-performance butterfly valves are constructed with more robust materials; they have increased temperature and pressure ratings, enhanced corrosion resistance, and improved sealing capabilities.
• Precise flow control: While they can be used for basic flow regulation, butterfly valves are not ideal for applications requiring precise flow control, as their design does not allow fine adjustments. They are commonly used when flow regulation is needed, and leakage isn't critical.
  • Triple offset butterfly valves offer enhanced sealing for applications where leakage is a concern, making them suitable for flow regulation and leak tightness. However, their flow control precision is generally less than that of valves like globe valves, which are designed for fine adjustments.
• Flow obstruction: The disc remains in the flow path even when fully open (as the disc is centrally mounted), which can cause a pressure drop and make it unsuitable for applications where minimal flow resistance is critical.
• Not piggable: Butterfly valves are unsuitable for systems requiring pigging (cleaning with a device that travels through the pipeline) because the disc obstructs the flow path.

Butterfly valves vs ball valves, gate valves, and globe valves

Butterfly valves are used for quick on/off applications and in low-pressure systems where cost and space efficiency are priorities. Other valve types, such as ball, gate, and globe valves, have unique features and are suited for different applications.

Table 1: Butterfly valve vs other valve types

Criteria Butterfly valve Ball valve Gate valve Globe valve Operation Quarter-turn Quarter-turn Multi-turn Multi-turn Flow control Good for on/off and throttling Excellent for on/off, not ideal for throttling Good for on/off, but not ideal for throttling Excellent for throttling and flow regulation Pressure drop Low Very low Low Moderate to high Space requirement Compact Compact Requires more space Requires more space Cost & maintenance Generally low, low maintenance Moderate to high cost, low to moderate maintenance Moderate cost, moderate maintenance Moderate to high cost, moderate to high maintenance Media suitability Suitable for slurry and viscous media Not suitable for slurry, suitable for viscous media Suitable for slurry and viscous media Not suitable for slurry, not ideal for viscous media Leakage Moderate (depends on seat design) Very low (tight shut-off) Low Moderate

Figure 3: Butterfly valve (top left), ball valve (top right), gate valve (bottom left), and globe valve (bottom right)

For more information on comparing a butterfly valve with other valve types, read our butterfly valve vs ball valve and gate valve vs butterfly valve articles.

FAQs

What does a butterfly valve do?

A butterfly valve regulates fluid flow through a pipe by rotating a disc to open, close, or partially obstruct the passage.

Can a butterfly valve be used for flow control?

Yes, a butterfly valve can be used for flow control. However, it may not provide as precise control as other types of valves, such as globe valves, especially at low flow rates.

When to use a butterfly valve vs a ball valve?

Use a butterfly valve for applications with slurry or viscous media with controlled flow and a ball valve for applications needing tight shut-off and minimal leakage with quick on/off control.

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What is the difference between a butterfly valve and a gate valve?

A butterfly valve uses a rotating disc for flow control, while a gate valve uses a sliding gate to open or close the flow path.

Butterfly valves are a family of quarter-turn rotational motion valves that are used in pipelines to shut-off flow. It is often said that butterfly valves can be used to regulate the flow. However, we do not recommend doing this, as it can damage the valve disk and have a negative effect on the sealing properties. They are used in a wide variety of process media and industries especially in water supply, collection, and distribution, as well as pumping stations, and have a broad range of use cases especially in flow isolation. A couple of their key advantages over other valve families are their simple construction and compactness, resulting in the end products being of lighter weights and lower cost and with smaller installation footprints and faster actuation speeds.

Hawle butterfly valves are flanged double eccentric type (double offset) type. The double offset or eccentricity refers to the fact that this valve design involves two offsets of the disc from the valve body’s centre or the axis of rotation of the stem.

Below are the major butterfly valve components:

• Valve Body
  The valve body fits between the pipe flanges - the most common end connection types being flanged, double lug, and wafer types.
   
• Disc
  Attached to the valve body is the disc that functions as a gate that stops or throttles fluid flow; it can be considered equivalent to a gate in a gate valve, or a ball in a ball valve. The disc is typically bored to receive the stem, or shaft. There are many variations in disc design, orientation, and material in order to improve flow, sealing, and/or operating torque. For example, Hawle’s k double eccentric disc is designed to reduce seal wear and “scuffing” as well as operating torque requirements.
   
• Seat
  Lining the internal valve body is a strong elastomer or metal anti-leak seal that secures the disc in place in the closed position in order to achieve complete shutoff. The k series’ stainless steel weld filled and microfinished integral body seat ensures a corrosion and erosion resistant seat face. With this special type of seat design, it is possible to manufacture the valve drop tight according to EN –A requirements.
   
• Stem
  The valve shaft, often also referred to as the stem, is the component that connects the disc to the actuation mechanism and transmits the torque through itself.
   
• Seals
  Seals are present at multiple interfaces within the valve to either ensure a tight seal during operation or to isolate the process media from the valve’s internal components for a more flexible and cost-efficient design.

Sealing on seat face is ensured by a continuous T-profile resilient sealing ring which is held on the periphery of the disc by a retaining ring, preventing the sealing ring from rolling out. In the closed position, the sealing ring is pressed against the seat face, providing a tight seal on both the upstream and downstream ends. In the open position, the sealing ring is completely unstressed due to the double eccentric disc design.

By eliminating interaction between the process media and the stem/shaft, the multiple O-ring shaft sealing system ensures a maintenance-free sealing for the entire life span of the valve. Besides, there are smaller more common components such as the bushings, bearings, and fasteners that are part of most other valve constructions as well. Details on some of the components on the actuation end, such as the handle, lever, gearbox, and handwheel will be covered in the actuation section.

The construction of a butterfly valve is relatively simple, with the rotation of the valve disc controlling the fluid flow. In the closed position, the disc blocks the valve bore while in the open position, the disc is oriented perpendicular to the flow direction to allow flow. Butterfly valves generally provide bi-directional flow and shutoff capability. However, they are not full-bore, which renders them unsuitable for pigging or swabbing. The body material is ductile iron with an epoxy powder coat on both internal and external surfaces. The valves are typically operated by handwheels, gears, or actuators, or a combination thereof, according to the specific application requirement and technical specifications. We will be discussing the actuation methods later in the article.

There are multiple ways to operate, or actuate, a butterfly valve - manual, semi-manual, or fully automatic.

• Electric: Uses an electric actuator for controlling the valve with a 4-20mA control signal and are typically used for high precision regulation and time-sensitive application.
   
• Pneumatic: Also used for high precision application and uses compressed air for actuation.
   
• Hydraulic: Typically used for applications requiring large torques for opening and closing the valve, such as high pressure and high viscosity applications.
   
• Manual: Manually operated butter valves make use of a handwheel, crank, or lever to operate the valve. Smaller manual valves are typically fitted with a lever. For larger sizes, handwheels are provided and are accompanied by a gearbox to transfer the torque with a high mechanical advantage. Another way of manual actuation is in use cases where the valve is buried underground without a manhole; in such applications, actuation is done with an extension spindle, adapter / square cap, and a corresponding T-key from the ground level.

Due to inherently lower torque requirements, sizing and installing actuators are less expensive for butterfly valves compared to others, like gate valves.

The k series comes standard with a handwheel actuation and wormwheel gearbox with a self-locking design feature that minimizes gear backlash and guarantees the correct operation and tightness of the end device. It is also compatible with external actuators with an ISO top flange for mounting of multi-turn actuators.

On the application side, butterfly valves are especially well-suited for the handling of large fluid flows of fluid, such as in water distribution systems (pumping stations or water collection and transmission) and water treatment plants (seawater or raw water). This, along with their availability in a large range of sizes including up to DN (55 inches), makes them ideal for drinking water distribution applications. They are typically used for flow isolation devices and are normally fully open or fully closed. Hawle provides butterfly valves geared towards specific application areas and are available on demand. The Özkan double eccentric double flanged butterfly valves, for example, are offered for high pressure applications upto 40 bar (PN 40) and up to DN .

The Hawle k series double eccentric butterfly valves come in sizes ranging from DN 150 up to DN with pressure ratings of both PN 10 and PN 16. Additionally, design feature optimizations such as the double offset, or double eccentric (e1 and e2 as seen above) disc further reinforces its advantages of achieving a tight seat seal through full circle sealing, and improves the service life of internal components while lowering operating torque requirements.

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