Butterfly Valve - How They Work

Butterfly valves are quarter-turn valves that are popular for on-off or modulating services. They are lightweight, have a small installation footprint, lower cost, quick operation, and are available with large orifice sizes. The “butterfly” is a disk connected to a rod. When the valve opens, the disk rotates to allow fluid to pass through. It closes when the rod rotates the disc by a quarter turn to a position perpendicular to the flow direction. Learn more about how Butterfly valves work and when to use them for different applications.

Below are the major Butterfly valves 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 9881k 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 9881k 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 EN12266 –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.

Applications

ball valve are used in diverse industries and applications such as pharmaceutical, chemical and oil, food, water supply, wastewater treatment, fire protection, gas supply, fuel handling, and sanitary fittings. ball valve for water are used as control valves in pipelines to shut off water flow. These valve are available in huge sizes and are suitable for handling slurries and liquids with relatively large amounts of solids at low pressures. Stainless steel butterfly valves are used in corrosive and marine environmental applications as the material is highly durable and resistant to corrosion.

Ball valve vs ball valve

Typically, a ball valve with similar characteristics to a ball valve is cheaper, easier to install, and has a smaller installation footprint. However, due to the disc in butterfly valves, they cannot be pigged for cleaning purposes. Ball valves are advantageous for high-pressure, small diameter applications as they are better suited for higher pressure differences and cause minimal pressure drop over the valve. ball valve have a relatively simple design with fewer moving parts and fewer pockets/traps for media. Therefore they are easier to repair and cheaper to maintain. For small pipe diameters a ball valve is typically better suited to the torque and cost. The torque and cost advantages of butterfly valve appear around DN 50 and upwards. Read our article on ball valves vs butterfly valves for a detailed comparison between both valve types.

butterfly valves are quarter-turn valves that are popular for on-off or modulating services. They are lightweight, have a small installation footprint, lower cost, quick operation, and are available with large orifice sizes. The “butterfly” is a disk connected to a rod. When the valve opens, the disk rotates to allow fluid to pass through. It closes when the rod rotates the disc by a quarter turn to a position perpendicular to the flow direction. Learn more about how butterfly valves work and when to use them for different applications.

Below are the major butterfly valves 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 9881k 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 9881k 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 EN12266 –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.

Applications

Butterfly valves are used in diverse industries and applications such as pharmaceutical, chemical and oil, food, water supply, wastewater treatment, fire protection, gas supply, fuel handling, and sanitary fittings. Butterfly valves for water are used as control valves in pipelines to shut off water flow. These valves are available in huge sizes and are suitable for handling slurries and liquids with relatively large amounts of solids at low pressures. Stainless steel butterfly valves are used in corrosive and marine environmental applications as the material is highly durable and resistant to corrosion.

Ball valve vs butterfly valves

Typically, a butterfly valves with similar characteristics to a ball valves is cheaper, easier to install, and has a smaller installation footprint. However, due to the disc in butterfly valves, they cannot be pigged for cleaning purposes. ball valves are advantageous for high-pressure, small diameter applications as they are better suited for higher pressure differences and cause minimal pressure drop over the valve. butterfly valves have a relatively simple design with fewer moving parts and fewer pockets/traps for media. Therefore they are easier to repair and cheaper to maintain. For small pipe diameters a ball valve is typically better suited to the torque and cost. The torque and cost advantages of butterfly valves appear around DN 50 and upwards. Read our article on ball valves vs butterfly valves for a detailed comparison between both valve types.