What is Butterfly Valve Disc and Why Do We Use Them?

Jun. 16, 2025

What is a Butterfly Valve? - Belimo

What is a Butterfly Valve?

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If you work in HVAC or plumbing, you’ve likely come across butterfly valves. But what defines them, and how do they differ from other valve types? A butterfly valve is a flow control device that uses a rotating disc to regulate or isolate fluid movement. Butterfly valves can handle large volumes with less space and weight compared to other valve types, making them a favorite in HVAC applications where efficiency and compactness matter. The word “butterfly” refers to the metal disc that turns within the pipe to open or restrict flow. With a simple 90-degree turn, the valve shifts from fully open to fully closed.

Why would you use a butterfly valve?

Butterfly valves are widely used in systems that require reliable shut-off and flow regulation without the footprint or complexity of bulkier valve types. They’re especially useful in large-diameter piping where minimizing pressure drop and weight is critical. Their simple mechanism allows for fast actuation, and with the right actuator, they’re well-suited for on/off, 3-point, or modulating control. In HVAC, this makes them ideal for chilled water, hot water, and condenser water systems where space, efficiency, and installation time are all important factors.

Why use a butterfly valve instead of a ball valve?

While ball valves also offer quarter-turn actuation, butterfly valves are generally more compact and lighter—especially in larger sizes. Ball valves become bulky and expensive as diameter increases, whereas butterfly valves maintain a slim profile and cost-effectiveness. Additionally, butterfly valves can be configured for tight shut-off and modulating control in large HVAC systems, where ball valves are typically favored for smaller, more localized applications. When you’re dealing with flow control in 4" or larger pipe, butterfly valves tend to offer better overall value.

Why use a butterfly valve instead of a gate valve?

Gate valves are designed for full open or full closed service, but they’re slower to operate and tend to have more maintenance issues over time due to sediment buildup in the gate track. Butterfly valves, by contrast, actuate quickly with a simple 90-degree turn and take up less space, making them easier to install in tight mechanical rooms. They also tend to provide a better seal in modern systems and offer more flexible control options when paired with actuators. For applications requiring frequent operation or remote actuation, butterfly valves are generally the better choice.

Why use a butterfly valve instead of a globe valve?

Globe valves are known for their precise flow control, but that precision comes at the cost of pressure drop, size, and weight. In HVAC systems, particularly those with large pipe diameters, a globe valve can be prohibitively heavy and expensive. Butterfly valves offer a compelling alternative: with proper actuator pairing, they can deliver equal percentage or linear flow control while minimizing pressure losses and taking up far less space. That’s one reason Belimo butterfly valves, in particular, are replacing globe valves in many high-performance systems.

What makes Belimo butterfly valves different?

Belimo’s advanced butterfly valve assemblies are specifically engineered for HVAC systems, offering a combination of smart design, high energy efficiency, and proven long-term reliability. They feature a patent-pending, self-adjusting end stop algorithm that delivers zero leakage at up to 200 psi close-off. The actuators use our patented brushless DC motor technology to reduce energy consumption by up to 80%, while the integrated high-performance processor enables precise flow control. Our compact actuator design allows for installation in tight spaces, and NFC functionality allows for fast commissioning, programming, and diagnostics, even without power. With proven performance across large flow applications and a five-year warranty, Belimo butterfly valves offer a durable, efficient solution for demanding HVAC systems.

How do Belimo valves help save energy?

This is one of the most common questions asked when people are considering an upgrade. The short answer is smart torque management. Belimo matches each butterfly valve with an actuator that is designed to deliver only the exact torque required. This reduces wasted energy, extends actuator life, and ensures consistent performance over time. Combined with low pressure drop and efficient design, Belimo butterfly valves make a meaningful contribution to overall energy savings across the system.

Are Belimo butterfly valves easy to install?

Ease of installation matters, especially when you're working in tight mechanical rooms or upgrading legacy systems. Belimo butterfly valves are much lighter and shorter than traditional globe valves. A 3-way 8-inch Belimo butterfly valve, for example, weighs less than half of what a similar-sized globe valve weighs and is half the height. That reduction in size and weight not only makes installation faster, it also places less physical strain on the piping system.

Can Belimo valves connect to building automation systems?

Yes. Belimo butterfly valves are designed for full compatibility with building automation systems through support for BACnet MS/TP, Modbus RTU, and Belimo’s MP-Bus protocols. The PR, PKR, and JR actuator series all include these communication capabilities, allowing seamless integration with most building management platforms. Each actuator series also features Near Field Communication (NFC), which enables quick programming, diagnostics, and commissioning without the need for power. This combination of connectivity and serviceability makes it easier to monitor, configure, and optimize valve performance directly from a centralized system.

Are Belimo valves compatible with sensors?

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Definitely. Belimo actuators support direct sensor inputs, which means you can wire sensors right into the actuator without needing to run them all the way back to the controller. This not only simplifies installation but also lowers costs by reducing wiring and setup time. It’s a design choice that supports smarter building designs and faster installations.

Are Belimo valves reliable in tough environments?

Durability is a big concern, especially in rooftop installations or damp mechanical spaces. Belimo butterfly actuators are built to NEMA 4X standards, meaning they can withstand dust, rain, and other challenging conditions. The valve bodies are ductile iron, and the internal discs are stainless steel, ensuring strength and corrosion resistance. These aren’t throwaway components. They’re built for the long haul.

Can Belimo butterfly valves provide precise control?

Yes, and that surprises a lot of people. These valves are not just on/off devices; they’re capable of both equal percentage and linear flow characteristics. That gives you the precision needed for variable flow applications and ensures your system responds smoothly to demand. With the Belimo Assistant 2 App, you can customize settings right from your , including adjusting CV values or modifying control curves.

Are Belimo butterfly valves worth it?

When you consider the full picture, including tight shut-off, energy savings, flexible installation, smart integration, and long-term reliability, it’s hard to argue against them. Belimo’s butterfly valves are a strong fit for HVAC pros looking for a future-ready system that avoids constant maintenance and complicated setup.

What is a butterfly valve and where it is used in water supply? - Hawle

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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