What is a Butterfly Valve? Types, Uses & How It Works
Choosing the right valve for a water storage tank system is one of those decisions that looks straightforward until you are standing in front of a specification sheet trying to decide between three different valve types. Get it right and your tank system operates efficiently, reliably, and safely. Get it wrong and you face pressure loss, flow control problems, or a valve that simply is not suited to the liquid or the pipe size you are working with.
Butterfly valves are one of the most widely used valve types across UK water storage, industrial, and agricultural applications, yet they are frequently confused with gate valves and ball valves. Each type serves a specific purpose. This guide explains what a butterfly valve is, how it works, the different types of butterfly valves available, what they are best suited to, and how to choose the right valve for your water storage tank application.
What is a Butterfly Valve?
A butterfly valve is a quarter-turn rotary valve used to regulate or isolate the flow of liquid through a pipe. Butterfly valve refers to the disc-shaped closure element at the centre of the valve body, which rotates on a shaft to open or close the flow path. When the valve is fully open, the valve disc sits parallel to the flow, allowing liquid to pass through with minimal resistance. When the valve is closed, the valve disc rotates ninety degrees so it sits perpendicular to the flow, blocking the pipe completely.
The butterfly valve is a quarter-turn valve, meaning a single ninety-degree turn of the actuator or handle moves it from fully open to fully closed. This makes butterfly valves fast to operate and simple to automate. Butterfly valves are lightweight, compact, and cost-effective compared to other valve types of equivalent bore size, which is why butterfly valves are widely used across water supply, wastewater, industrial, and agricultural systems throughout the UK.
Unlike a gate valve, which uses a sliding gate inside the valve body, or a ball valve, which uses a rotating ball with a hollow bore, a butterfly valve uses a disc that remains within the valve bore at all times. This is the key design characteristic that defines butterfly valve performance and determines when it is the right choice for a given application. Butterfly valves tend to be the preferred choice where compact size, fast operation, and flow regulation capability are all required in a single fitting.
Components of a Butterfly Valve
Understanding the main butterfly valve components and butterfly valve parts helps with both selection and maintenance. The key components of a butterfly valve are the valve body, the valve disc, the stem, the seat, and the actuator or handle.
The valve body is the outer shell that connects to the pipe at each end and houses all internal components. Butterfly valve bodies are available in several end connection types depending on the installation. Wafer type butterfly valves sit between two pipe flanges and are held in place by through-bolts, making them the most compact and lightweight option. The valve is installed between two flanges with bolts passing through both flanges and the valve body on each side. Lug type butterfly valves have threaded inserts around the butterfly valve bodies that allow the valve to be bolted independently to each pipe flange, so the valve can be removed without disturbing the rest of the pipework. Flanged butterfly valves have integral flanges that bolt directly to matching flanges on the pipe, making them the most secure connection type for high-pressure or critical applications.
The valve disc is the rotating closure element positioned at the centre of the valve body. It is fixed to the stem and rotates within the valve body to open or close the flow path. The sides of the valve disc contact the seat when the valve is in the closed position, creating the seal that stops flow. The sides of the valve body guide the disc through its rotation and define the bore through which liquid flows when the valve is open. The design of the valve disc is what distinguishes the different types of butterfly valves from one another.
The seat is the sealing surface inside the valve body against which the disc presses when the valve is closed. The seat material determines the chemical compatibility of the valve with the liquid being controlled and the quality of the seal in the closed position.
The stem connects the disc to the actuator or handle. Butterfly valve actuation can be manual via a lever or gearbox handwheel, or by an actuated butterfly valve using a pneumatic, hydraulic, or electric actuator for applications where the valve needs to be operated remotely or as part of an automated control system. Valve automation is particularly common on larger butterfly valves used in systems that require remote operation or integration with a site control system.
Types of Butterfly Valves
Not all butterfly valves are the same. The three types of butterfly valves differ in the design and offset of the disc relative to the stem and seat, which directly affects sealing performance, pressure rating, and suitability for different applications. Butterfly valves come in concentric, double offset, and triple offset body types, and butterfly valves are available across all three designs in a wide range of sizes and materials to suit different systems and operating conditions.
Concentric Butterfly Valves
Concentric butterfly valves, also called centric butterfly valves or zero-offset butterfly valves, are the most common and cost-effective type. The stem passes through the centre of the disc, which sits centrally within the valve bore. When the valve closes, the disc presses against a resilient rubber seat that wraps around the entire inner surface of the valve body.
Centric butterfly valves are suitable for low to medium pressure applications involving clean water, non-aggressive liquids, and general water supply systems. They are the standard choice for water storage tank outlet connections, irrigation systems, rainwater harvesting installations, and general water distribution pipework. Their lightweight construction and simple design make them easy to install and maintain, and butterfly valves can be operated manually or with basic actuators in most standard applications. Butterfly valves are suitable for a wide range of general water supply and storage duties at this concentric design level.
Double Offset Butterfly Valves
Double offset butterfly valves, also called double eccentric butterfly valves or high-performance butterfly valves, have the stem offset from both the centre of the disc and the centreline of the pipe bore. This double-offset design means the disc lifts away from the seat as it opens rather than sliding across it, which dramatically reduces seat wear and allows the valve to handle higher pressures and more aggressive media than a concentric design.
Double eccentric butterfly valves are used in systems that require tighter shut-off performance and longer service life, particularly in industrial process pipework, chemical handling systems, and larger water distribution infrastructure. The double-offset butterfly valve is a common choice where valve performance needs to be maintained across frequent operation cycles. These are longer valve designs than standard concentric types and butterfly valves typically of this kind are specified where durability under demanding conditions is the priority.
Triple Offset Butterfly Valves
Triple offset butterfly valves, also called triple eccentric butterfly valves, add a third offset to the disc geometry, creating a cone-shaped sealing surface that achieves metal-to-metal contact between the disc and seat when closed. This makes the triple offset butterfly valve the highest-performance option available, capable of handling high pressures, high temperatures, and highly aggressive media including steam, acids, and hydrocarbons.
Triple eccentric butterfly valves are found in oil and gas, power generation, and chemical processing applications where absolute shut-off and extreme durability are the priority. For most water storage and agricultural applications, a concentric or double offset butterfly valve provides the performance required at a significantly lower cost. The different types of butterfly valves across these three body types of butterfly valves cover every application from basic water storage to the most demanding industrial process duty.
How Does a Butterfly Valve Work?
A butterfly valve works through a simple and direct rotational mechanism. When the handle or actuator turns the stem, the valve disc rotates within the valve body. As the disc moves from the closed position, where it sits perpendicular to the flow, toward the open position, where it sits parallel to the flow, the restriction to flow through the pipe decreases progressively. To open the valve, the operator turns the handle or actuator a quarter turn anticlockwise. To close the valve, the same quarter turn in the reverse direction returns the disc to the sealed position. The valve is fitted with a position indicator on most manual and actuated designs so the operator can confirm whether the valve is open or closed at a glance.
This is an important characteristic that sets butterfly valves apart from gate valves and ball valves. Because the disc can be held at any angle between fully open and fully closed, butterfly valves are used to regulate or throttle flow as well as to isolate it completely. Butterfly valve controls flow continuously across the full range of disc positions, not just at the two extremes, making butterfly valves suitable for applications where precise flow regulation matters alongside simple on/off isolation.
Within the valve body, the valve disc always remains in the flow path, even when the valve is fully open. This creates a small but permanent pressure drop across a butterfly valve that does not exist with a full-bore gate valve or ball valve. For most water storage tank applications this pressure drop is acceptable and is outweighed by the advantages of compact size, low weight, and ease of actuation that butterfly valves offer. Butterfly valves cannot provide the completely unobstructed bore of a full-bore gate valve, but for the vast majority of water storage and flow control applications this is not a practical limitation.
Butterfly Valve vs Gate Valve vs Ball Valve
All three valve types are available as standard fittings for Butek Tanks corrugated steel water storage tanks through our accessories range, in inlet and outlet sizes from 2 inches to 12 inches. Selecting the right type depends on the pipe size, the liquid being controlled, how frequently the valve will be operated, and whether flow regulation or simple isolation is the requirement.
Butterfly valves are generally the best choice for larger bore pipe connections where space and weight are considerations, where flow regulation is needed alongside isolation, and where the valve will be operated regularly. Butterfly valves can handle large diameter connections more cost-effectively than gate valves of the same size, and their quarter-turn operation makes them faster and easier to automate. Butterfly valves are widely used in systems that require both on/off control and variable flow regulation from a single fitting, and advanced butterfly valve designs with actuators are available for fully automated installations.
Gate valves remain the preferred choice for full-bore isolation on larger pipelines where zero pressure drop in the open position is critical and where the valve will be operated infrequently. A gate valve has no disc obstruction within the bore when fully open, which a butterfly valve always has.
Ball valves are best suited to smaller bore connections requiring frequent operation and fast quarter-turn shut-off. Ball valves offer a full-bore design like gate valves but in a compact, lightweight body suited to smaller pipe diameters.
Butterfly Valves in UK Water Storage Tank Applications
Butterfly valves are commonly used across a wide range of UK water storage and liquid management applications. Butterfly valves are versatile enough to be used on potable water, rainwater, effluent, slurry, and industrial process systems, which is why butterfly valves include such a broad range of seat materials, body materials, and actuation options to suit different liquids and operating conditions. On Butek Tanks corrugated steel water storage tanks, butterfly valves are typically specified on larger outlet and drain connections where their compact body size, quarter-turn operation, and ability to regulate flow make them the practical choice.
Common applications where butterfly valves are widely used alongside Butek Tanks products include potable water storage tank outlet connections, rainwater harvesting tank drain valves, effluent storage tank primary outlets, slurry and digestate tank discharge connections, irrigation water storage system outlets, and flow control between interconnected tank systems in aquaculture and industrial process water applications. Butterfly valves can handle large flow volumes on these connections cost-effectively, and butterfly valves are available in stainless steel body and disc options for corrosive or hygienic applications.
For potable water systems, butterfly valves used in water supply must be WRAS-approved under the Water Supply (Water Fittings) Regulations 1999. Stainless steel butterfly valves or valves with food-grade approved seat materials are the correct specification for tanks fitted with a Butyl rubber liner for drinking water storage. For effluent and slurry storage systems, butterfly valves with chemically resistant seat materials are required to match the Landflex ES liner specification used on those tanks.
Valve selection is always part of the overall tank design at Butek Tanks. Our team specifies butterfly valves, gate valves, and ball valves as part of a complete tank solution matched to the liquid, the pipe size, and the application, ensuring every component works together from installation through to long-term operation.
Frequently Asked Questions About Butterfly Valves
What is a butterfly valve used for?
A butterfly valve is used to regulate or isolate the flow of liquid through a pipe. Butterfly valves are suitable for both on/off isolation and flow throttling, making them more versatile than gate valves in applications where precise flow control matters. They are widely used in water supply systems, water storage tank outlets, irrigation pipework, effluent discharge connections, and industrial process pipework.
What are the three types of butterfly valves?
The three types of butterfly valves are concentric butterfly valves, double offset butterfly valves, and triple offset butterfly valves. Concentric butterfly valves are the standard choice for water storage and general water supply applications. Double eccentric butterfly valves suit higher-pressure and more demanding applications. Triple eccentric butterfly valves are used in systems that require metal-to-metal sealing at high pressures and temperatures.
What is the difference between a wafer and a lug butterfly valve?
Wafer butterfly valves sit between two pipe flanges held together by through-bolts and are the most compact and lightweight connection type. The valve is installed between two flanges with bolts passing through the full assembly. Lug type butterfly valves have threaded inserts in the butterfly valve bodies that allow each side of the pipe to be bolted independently to the valve, meaning the valve can be removed for maintenance without disturbing the rest of the pipework.
Can a butterfly valve regulate flow?
Yes. Unlike gate valves, which are designed for fully open or fully closed operation only, butterfly valves are used to regulate or throttle flow across the full range of disc positions. This makes butterfly valves suitable for applications where controlling the rate of flow matters, not just stopping it completely.
What is the difference between a butterfly valve and a ball valve?
Both butterfly valves and ball valves are quarter-turn valves, but they work differently. A ball valve uses a rotating ball with a full-bore hole drilled through it, giving zero pressure drop when fully open. A butterfly valve uses a valve disc that remains in the flow path even when fully open, creating a small pressure drop. Ball valves are generally better for smaller bore connections and full-bore shut-off. Butterfly valves are generally better for larger bore connections where compact size, light weight, and flow regulation capability matter.
Are butterfly valves suitable for slurry and effluent?
Butterfly valves can be used on slurry and effluent systems when fitted with appropriate seat materials resistant to the chemical and abrasive properties of the stored liquid. For highly viscous or heavily contaminated slurry, a knife gate valve is often the more appropriate choice. Our team specifies the correct valve type and seat material for each application as part of the tank design process.
Conclusion
A butterfly valve is a versatile, compact, and cost-effective quarter-turn valve that controls flow in a wide range of water storage and liquid management applications. Understanding the different types of butterfly valves and how they compare to gate valves and ball valves ensures the right valve is specified for every connection on your tank system, whether you are storing potable water, effluent, slurry, rainwater, or any other liquid.
At Butek Tanks, we have been designing and manufacturing corrugated steel storage tanks since 1965. Our accessories range includes butterfly valves, gate valves, and ball valves in all sizes and materials, specified as part of a complete tank solution alongside our liner kits and roof kits. Contact our team today to arrange a free site survey.