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Butterfly Valves: Construction, Types & Advantages

Exploded view of butterfly valve parts: body, disc, stem and seat
Butterfly valves are quarter-turn valves in which a rotating disc controls flow through a pipeline. They are widely used for isolation tasks in water distribution, pumping stations and other water facilities because of their compact design, low weight and relatively low cost. Although some resilient-seated butterfly valves can be used for limited flow control, as a general rule avoid continuous throttling with a standard butterfly valve because partial opening can increase disk wear and impair sealing performance.
Flange Butterfly valves

Flange Butterfly valves

Butterfly valves are flanged, double eccentric (double offset) designs. Double eccentric means the disc rotation axis is offset from the pipe centre in two places: one offset moves the shaft away from the bore axis and the second shifts the disc off the body centre, which reduces rubbing during opening and closing and improves sealing life.

Butterfly valve parts

Parts Butterfly valves

Parts Butterfly valves

The following are the principal components of butterfly valves, with brief notes on common materials and practical selection tips.
  • Valve body
  • The body houses the disc and seat and is the pressure-retaining part that fits between pipe flanges. Typical materials are ductile iron (with internal epoxy coating for potable water), carbon steel or stainless steel for corrosive or high-temperature services. Choose metal bodies for high-pressure and abrasive services; for many water treatment and distribution applications a ductile iron body is appropriate.
  • Disc
  • The disc is the element that stops or throttles flow. Discs are commonly steel, ductile iron with a coating, or stainless steel for aggressive media. Disc design variations (profiled, reduced bore, or grooved) influence flow, torque and sealing. For example, thedouble-eccentric disc is engineered to reduce seal wear and scuffing and to lower operating torque requirements.
  • Seat
  • Seats form the sealing face between disc and body. Options include resilient elastomeric seats (EPDM, NBR, etc.) for resilient seated butterfly valves and metal or weld-faced seats for higher temperatures, pressures and abrasive media. The 9881k series uses a stainless-steel weld-filled, microfinished integral body seat to provide corrosion and erosion resistance and allows manufacture to EN12266‑A (drop-tight) where required. When selecting seats, balance sealing performance against media compatibility and operating pressures.
  • Stem / shaft
  • The stem (or shaft) transmits torque from the actuator to the disc. Materials are usually stainless steel or other corrosion‑resistant alloys; double-eccentric designs offset the shaft to reduce rubbing and torque. Ensure stem material and shaft sealing are compatible with the process media.
  • Seals and O‑rings
  • Seals are located at multiple interfaces. A continuous T‑profile resilient sealing ring is commonly used on resilient-seated designs: it is retained around the disc periphery and presses against the seat face to achieve tight shutoff. In double-eccentric valves the ring is unloaded when the disc is open, reducing wear. Shaft sealing commonly uses multiple O‑rings or lip seals; these isolate process media from bearings and the actuation mechanism.
Practical notes: resilient seated butterfly valves are an economical choice for water treatment and distribution services where tight shutoff and low leakage are required at moderate pressures. For abrasive, high-temperature or high-pressure applications consider metal seats or weld-faced seats. Claims such as “maintenance-free for the entire lifespan” depend on application, media and duty cycle — specify expected operating years and maintenance intervals when placing an order.
Smaller components—bushings, bearings and fasteners—support the main parts, and actuation-end components (handle, lever, gearbox and handwheel) will be covered in the actuation section. For standards and compliance, consult the product datasheet (links preserved above) and EN12266 for testing and leakage classes.

Butterfly valve: working principle

Butterfly valves control flow by rotating a disc through a 90° arc: aligned with flow when open, and transverse to flow when closed. This simple quarter-turn operation gives quick on/off performance and bi-directional shutoff in most designs. Because butterfly valves are not full-bore, they are generally unsuitable for pigging or swabbing operations where an unobstructed bore is required.
Body materials vary with application: many water distribution valves use ductile iron bodies with an internal epoxy powder coat for potable-water service, while stainless steel or other alloys may be selected for corrosive or treatment‑plant environments. Note: material depends on the valve model and service requirements — consult the product datasheet for specific body options and compatibility.
Typical means of operation include handwheels, gearboxes, or powered actuators. For a concise guide to actuator selection see the actuation section (anchor: #toc-04). When using a butterfly valve for any degree of flow control rather than pure isolation, choose a resilient‑seated or purpose‑designed control butterfly valve and verify the required control characteristics (Kv/Cv) and seat wear behaviour.

Butterfly valve actuation

Butterfly valves can be actuated manually or by powered systems; choice depends on the application, required response time and control needs. Actuation falls broadly into four categories: electric, pneumatic, hydraulic and manual. Select the actuator that matches torque, speed and control requirements for the valve size and service.
  • Electric
  • Electric actuators are common where remote or automated control is needed. They typically accept control signals (for example 4–20 mA for positioners) and are suitable for on/off and modulating control when paired with a positioner and suitable control butterfly valve trim. Use electric actuators in treatment plants and distribution systems where precise control and integration with SCADA are required.
  • Pneumatic
  • Pneumatic actuators use compressed air and offer fast response and simple fail-safe options (spring return). They are often chosen where electrical safety is a concern or where compressed air is readily available.
  • Hydraulic
  • Hydraulic actuators deliver high torques and are appropriate for very large valves or high-pressure applications where large mechanical forces are required.
  • Manual
  • Manual actuation uses handwheels, levers or cranks. Small valves often have levers; larger sizes use handwheels with gearboxes to reduce operator effort. Where valves are buried, extension spindles, square caps and T‑keys provide remote manual access (see accessories link above).
Actuator selection checklist (brief): required torque at operating pressure; desired speed of operation; control type (on/off or modulating); control signal and integration (e.g. 4–20 mA for electric positioners); fail‑safe requirement (spring return); and environmental/service conditions. Because butterfly valves generally need lower operating torque than gate valves, actuator sizing and installation are often simpler and less costly — but always calculate torque with seat and media conditions in mind.
The 9881k series is supplied with a handwheel and wormwheel gearbox featuring a self‑locking design to reduce backlash and maintain tightness. It is also compatible with external actuators using an ISO 5210 top flange for standardised actuator mounting. For actuator sizing assistance, contact our engineers who can advise on installation and performance requirements.
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Advantages of butterfly valves

Butterfly valves offer clear benefits in many applications, particularly for larger diameters (commonly DN 200 and above) used in water distribution and treatment. Their principal advantages are:
  1. Lightweight and compact: Butterfly valves have a small face‑to‑face dimension and compact body, reducing installation footprint, support structures and labour compared with larger gate or ball valves — a direct saving in installation cost for mains and plant piping.
  2. Low maintenance: With fewer moving parts and a simple construction, butterfly valves generally require less routine maintenance and present fewer wear points, improving lifecycle performance in water and treatment services.
  3. Fast acting: A 90° rotation provides full open or closed positions, enabling quick isolation. For very large valves a gearbox is used to reduce operating torque; this trades speed for operator effort where required.
  4. Cost‑effective: The simple design commonly uses less material and manufacturing time than other valve types, making butterfly valves an economical choice particularly in larger sizes (frequently above DN 300).
  5. Versatility: Available in a wide variety of configurations (wafer, lug, double‑flanged), materials and seat types, butterfly valves suit many applications and can be adapted for buried or above‑ground installation when specified appropriately.
When to choose another valve: butterfly valves are not full‑bore and therefore unsuited to pigging, swabbing or services requiring an unobstructed bore. They are also less suitable for highly abrasive slurries unless a robust disc/seat material is selected. For modulating control, choose resilient‑seated or purpose‑designed control butterfly valves and check the required control characteristics (Kv/Cv) and seat wear behaviour before selecting.
Practical example: for a DN 500 water main the reduced weight and smaller installation footprint of a butterfly valve can reduce civil and support costs compared with a knife gate or flanged ball valve; however, always assess pressures, media and operating cycles. For a tailored ROI estimate or assistance with valve selection and manufacturing options, request a quote from our technical sales team.

Double-eccentric  butterfly valves

On the application side, butterfly valves are especially well-suited for the handling of large fluid flows, such as in water distribution systems (pumping stations or water collection and transmission) and water treatment plants (seawater or raw water). Their availability across a wide range of sizes makes them ideal for drinking water distribution and other large‑flow applications. They are typically used for flow isolation and are normally specified to operate fully open or fully closed; select resilient seated butterfly designs when low leakage is required.
We offers models for demanding applications. The double eccentric double-flanged valves are available for high-pressure services (up to PN 40) and very large sizes on request. This type covers DN 150 to DN 1600 at PN 10 and PN 16 and features double offset (e1 and e2) geometry that helps achieve effective full‑circle sealing, longer service life and reduced operating torque.
How to choose: match valve size and body material to processing or treatment plant requirements, select seat type for media and pressure, and ensure actuator sizing meets torque and performance requirements. For gas applications or specialised services check approvals and material specifications. For precise model specifications, datasheets and case studies, or to request a quote and actuator sizing support, contact our technical sales team.
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