Lug butterfly valves occupy a critical niche in fluid control systems, bridging the gap between compact wafer valves and heavy-duty flanged valves.
Characterized by threaded “lugs” (bosses) integral to the valve body, used to bolt the valve directly to pipeline flanges,
They offer unique advantages: independent installation (no need to disassemble pipelines), bidirectional flow capability, and the option for blind flange mounting.
Unlike wafer valves (clamped between flanges) or flanged valves (with integral flanges), lug butterfly valves balance space efficiency, leak tightness, and ease of maintenance—making them ideal for medium-to-high pressure applications where valve removal without pipeline disassembly is critical.
1. What is a Lug Butterfly Valve?
Eräs raahata läppäventtiili is a quarter-turn rotary isolation valve whose body incorporates integral, kierteinen lugs around the bore so the valve can be bolted to mating flanges.
The lug configuration permits single-side flange removal (end-of-line installation), straightforward servicing and flexible mounting while retaining the compact, high-flow characteristics of a butterfly valve.
Basic anatomy and operating principle
A lug butterfly valve functions through the coordinated action of several principal components.
The table below summarizes each component with its typical design detail (nominal ranges) ja primary role.
| Komponentti | Typical design detail (nominal ranges) | Primary role |
| Vartalo | Cast or forged body with 4–12 integral lugs (threaded bosses) spaced to flange bolt circles; wall/throat thickness varies with size & paine (suunnilleen. 6–50 mm across common ranges). | Pressure boundary; provides mounting points and alignment for pipeline flanges. |
| Levy | Circular plate sized to ≈90–98% of bore (reduced-bore variants exist); thickness scales with diameter (≈3 mm to several tens of mm); profiilit: tasainen (concentric), contoured, convex (eccentric). | Rotates 0°→90° to modulate or isolate flow; primary flow obstruction and sealing partner for resilient seats. |
| Istuin | Resilient ring, PTFE/filled PTFE insert or metal seat; may be bonded, snap-in, or overmolded; cross-section and contact geometry vary by design. | Provides sealing surface; determines leakage performance, seating torque and temperature/chemical limits. |
Varsi / Akseli |
Solid or hollow stem sized to transmit required torque; includes anti-blowout shoulders or retention features; typical diameters range from ≈12–50 mm depending on valve size. | Transmits torque from actuator to disc; locates disc and houses sealing elements to atmosphere. |
| Lugs | Threaded bosses (bolt sizes typically M12–M30 or imperial equivalents) positioned per flange standards and increasing in quantity with diameter. | Allow bolting to flanges and end-of-line installation; transfer flange loads (but valve must not be used as pipe support). |
| Toimilaite / Handle | Manual lever/gearbox or powered actuator (sähköinen, pneumaattinen, hydraulinen); mounting per ISO 5211 interface; torque outputs from ≈10 N·m up to several kN·m. | Provides operating torque and control for on/off or modulating operation; enables remote/automatic control where required. |
Operating mechanism and practical performance data
Quarter-turn operation (0° → 90°):
- Fully open (≈0°): the disc is parallel to flow; flow area nearly unobstructed → low pressure drop. Esimerkki: a 6-inch lug butterfly at nominal flow may show ΔP in the order of 0.03–0.2 bar (0.5–3 psi) depending on disc profile and flow rate.
- Kaasu (≈10°–80°): partial rotation progressively reduces effective area.
Flow vs angle is epälineaarinen; concentric (zero-eccentric) discs have a more pronounced curvature in the characteristic, while eccentric designs provide a nearer-linear characteristic and lower seat wear.
Typical linearity approximations (indicative): concentric ±15% deviation, eccentric ±5% (these are approximate and depend on trim/profile). - Fully closed (≈90°): disc engages seat to stop flow. Resilient seats can provide bubble-tight shutoff for many services; metal seats are used where temperature/erosion demands exceed elastomer capabilities.
Bidirectional capability: Many lug butterfly valves can be used in either flow direction (subject to seat geometry and installation instructions).
This bidirectionality is useful in backwashing or reversible systems — but verify manufacturer guidance for critical services.
2. Design Variations: Concentric vs. Eccentric Lug Butterfly Valves
Butterfly-valve behavior and suitability for a task are strongly determined by the disc/stem geometry relative to the bore.
In lug butterfly valves the three principal geometric families are concentric (zero-eccentric), double-eccentric (offset), ja triple-eccentric (double-offset + conical seating).
Concentric Lug Butterfly Valve — simple and economical
Geometria & principle
- Stem axis coincides with the pipe bore axis and the disc is centered in the bore.
- The disc contacts the seat with full perimeter interference when closed (resilient seat typically compressed by disc).
Concentric Lug Butterfly Valve
Ominaispiirteet & suorituskyky
- Paras jhk: low-to-moderate pressure, low-temperature services; vettä, LVI, non-aggressive liquids and gases.
- Tiivistys: resilient seats (EPDM, NBR, FKM) give bubble-tight shutoff (practical Class VI behavior in many cases).
- Torque: relatively high seating torque because the disc scrubs against the seat during every cycle.
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- Typical seating torque multiplier vs. off-seat torque: seating can increase torque by 2–5× depending on seat durometer and line pressure.
- Kaasu: poor linearity; not recommended for fine control — flow vs angle non-linear (large curvature).
- Käyttää: seat abrasion and extrusion risk with particulates; limited temperature capability (seat-limited).
When to specify
- Municipal water lines, HVAC isolation, low-cost general purpose isolation up to ~PN16/ANSI150 and service temperatures within seat limits (ESIM., ≤120–150 °C for many elastomers).
Double-eccentric Lug Butterfly Valve — lower friction, better control
Geometria & principle
- Shaft axis is offset from the disc center and/or seat axis (two offsets): one offset moves the shaft behind the sealing surface; the second offsets the shaft radially to reduce rubbing.
- Disc first moves out of the seat with a cam-like action, reducing rubbing during operation.
Double Eccentric Lug Butterfly Valve
Ominaispiirteet & suorituskyky
- Paras jhk: applications needing better throttling control, reduced wear and longer seat life — common in chemical, petrochemical and process plants.
- Tiivistys: can be resilient or metal-seat; resilient seat life significantly improved over concentric.
- Torque: lower operating torque during travel (reduced rubbing), but still requires seating torque at final closure. Seating torque multiplier smaller than concentric (usein 1.2–2×).
- Kaasu: improved linearity and reduced hysteresis; usable for coarse to moderate control when paired with positioner.
- Käyttää & luotettavuus: less seat abrasion, better cycle life; improved performance with suspended solids vs concentric designs.
When to specify
- Process plants where some modulation is needed, slurry handling (with appropriate seats), and applications at higher temperatures or pressures where extended seat life is required.
Triple-offset Lug Butterfly Valve — metal-seated, high-performance isolation
Geometria & principle
- Two radial offsets plus a third offset that creates a true conical (or decentered cone) seating geometry.
The disc and seat engage on a single line of contact at final closure — virtually no rubbing before full shutoff. - Contact is metal-to-metal (or metal backed with a soft insert) and is designed to avoid frictional wear during rotation.
Triple Offset Lug Butterfly Valve Components
Ominaispiirteet & suorituskyky
- Paras jhk: high temperature, korkea paine, abrasive or erosive media, and applications requiring tight shutoff with metal seats (öljy & kaasu, power, high-temp steam).
- Tiivistys: metal seats (Stelliitti, hardfacing) provide tight shutoff; fire-safe by design.
- Torque: lowest dynamic torque during travel since disc does not rub the seat, mutta final seating torque can be high for metal closure and often requires actuators sized accordingly.
- Kaasu: not intended for continuous throttling; designed primarily for reliable isolation and severe service.
- Kestävyys: excellent for thermal cycling and abrasive flows; metal seats withstand >250–400 °C and beyond depending on materials.
When to specify
- High temperature steam isolation, subsea and upstream oil & gas service, hot hydrocarbon lines, turbine bypasses and wherever fire-safe, metal-to-metal sealing is mandated.
3. Materials of Lug Butterfly Valves
Material choice is the single most influential decision in a lug butterfly valve specification.
It determines corrosion resistance, temperature capability, mekaaninen lujuus, manufacturability and total life-cycle cost.
Material families — quick reference table
| Komponentti | Common material families | Typical service temperature (approx.) | Why chosen (key attributes) |
| Vartalo | Rauta- rauta, valurauta, hiiliteräs, cast stainless (CF8/CF8M), duplex/super-duplex, nikkeliseokset (Kattaa), bronze/bronze alloys | −40 °C → +600 ° C (varies by alloy) | Structural pressure boundary, cost vs corrosion resistance tradeoff |
| Levy / Leikata | 316/316Lensi, dupleksi, Hastelloy, pronssi, coated carbon steel, hardfaced alloys | −200 °C → +700 ° C | Erosion & corrosion resistance at the flow face; stiffness to resist deformation |
| Varsi / Akseli | 416/410 Ss, 17-4 PHE, 316/316Lensi, duplex stainless | −40 °C → +400 ° C | Vahvuus, torsion resistance, anti-galling capability |
| Istuin | Elastomeerit (EPDM, NBR), FKM (Viton), Ptfe (Teflon), filled PTFE, reinforced PTFE, metalli (Stellite®/hardfacing) | Elastomeerit: −40→+150 °C; Ptfe: −200→+260 °C; Metalli: +250→+600+ °C | Sealability, kemiallinen yhteensopivuus, temperature limit |
| Pinnoitteet / Linings | Epoksi, fusion bonded epoxy (FBE), rubber lining, PTFE lining, thermal spray hardfacing | Depends on coating (typ. jopa 300 °C for many) | Korroosiosuojaus, eroosiokestävyys, alhainen kitka |
4. Manufacturing Methods of Lug Butterfly Valve
Casting methods
Hiekkavalu (vihreä hiekka / hartsi-)
- When used: ductile iron or carbon steel bodies for municipal, HVAC and many industrial valves; best for large sizes and low-to-medium production volumes.
- Edut: low tooling cost, large part capacity, quick tooling lead time.
- Tyypilliset toleranssit: ±1.0–3.0 mm on gross dimensions; critical surfaces machined to final.
- Foundry notes: control riser and gating to avoid porosity at lug bosses and stem bore; use chills and directional solidification for lug integrity.
Investointi (lost-wax / ceramic shell) valu
- When used: stainless steel or low-defect bodies for chemical, meren-, and hygienic valves; small-to-medium parts where surface finish and dimensional accuracy matter.
- Edut: parempi pintakäsittely, thin sections, tighter tolerances (seat faces close to net), good for CF8/CF8M alloys.
- Tyypilliset toleranssit: ±0.1–0.5 mm on many dimensions after finish machine.
- Foundry notes: recommended for metal-seat or high-corrosion trims; requires pattern & shell cycle time (lead time 6–12 weeks for new tooling).
Taonta + koneistus
- When used: high-integrity forged bodies for high pressure or safety-critical applications.
- Edut: paremmat mekaaniset ominaisuudet (grain flow), lower risk of casting defects.
- Foundry notes: higher material and machining cost, used when service demands justify.
Hybridi & AM-enabled approaches
- 3D-printed patterns/cores: nopea prototyyppi, reduced tooling cost for low-volume parts.
- Printed sand cores: enable complex internal geometries (rare for lug valves but useful for special trims).
- Direct AM metal parts: possible for small valves or highly complex trims; limited by cost and build size.
Koneistus & finishing — tolerances and surface targets
Critical machined features
- Seat bore face (seal plane): typical finish target Ra ≤ 1.6 µm for resilient seats; Ra ≤ 0.8 µm for metal seats. Dimensional tolerance often ± 0,1 mm (check spec).
- Stem/shaft bore: concentricity to seat bore usually ≤ 0.1–0.2 mm TIR (total indicator reading) to avoid eccentric loading.
- Lug faces / bolt holes: tolerance to flange bolt circles per ASME B16.5; hole thread fit per ANSI/ISO standards.
- Disc profiling & balancing: trim to design contour; balance drilling or counterweights used on larger discs to control torque and reduce hydrodynamic loads.
Heat treatment — objectives and typical regimes
Heat treatment improves mechanical properties, relieves stress, or prepares surfaces for further processing. Esimerkit:
- Cast ductile iron: stress-relief anneal or normalizing as required (typical stress-relief at 550–650 ° C for several hours).
- Cast stainless (CF8/CF8M): solution anneal ≈1,040–1,100 °C followed by quench for corrosion resistance (per alloy spec).
- 17-4PH stems: solution treatment around 1,040 ° C, followed by aging (sademäärä kovettuminen) at 480–620 °C to reach required hardness (ESIM., 28–42 HRC depending on aging).
- Post-weld heat treatment (PWHT): may be required for welded assemblies per material spec and code.
Pintakäsittely, vuori & pinnoitteet
Common options & engineering targets
- Fusion-bonded epoxy (FBE): internal/external corrosion protection for carbon steel/ductile iron. Typical cure temps 180–230 °C. Coating thickness 150–300 µm.
- Vulcanized rubber lining: for abrasive or acidic services; bonding controls and cure cycles critical (typical cure temps 140–180 °C).
- PTFE liners / seat inserts: pressed or molded; ensure controlled interference fit and heat-lamination where required.
- Thermal spray (HVOF / plasma) hardfacing: WC-Co or NiCr overlays for erosion resistance on disc faces or seats; typical thickness 100-500 µm.
- Electroless nickel / hard chrome: to reduce friction and improve wear; thicknesses 5–25 µm yleinen.
5. Paineluokitukset, Sizes and Standards
Typical Size Range and Usage
Lug butterfly valves are widely manufactured in diameters ranging from DN50 (2″) DN1200 asti (48″) for standard industrial and municipal applications.
Specialized designs can reach DN2000 (80″) and above, especially in water distribution and power plants.
| Nimellinen halkaisija (DN) | Koko (tuuma) | Tyypilliset sovellukset | Muistiinpanot |
| DN50–DN150 | 2″–6″ | HVAC systems, elintarvikekäsittely, chemical dosing lines | Compact design; often lever-operated; suitable for low-to-medium pressure |
| DN200–DN600 | 8″–24″ | Municipal water treatment, öljy & gas process lines, kemialliset tehtaat | Most widely used size range; typically gear-operated or automated |
| DN700–DN1200 | 28″–48″ | Power plant cooling water systems, marine ballast systems, large-scale water distribution | Require gearboxes or actuators; high torque requirements |
| DN1300–DN2000 | 52″–80″ | Hydropower stations, seawater intake lines, large municipal water networks | Heavy-duty construction; customized; transport and installation logistics critical |
| DN2000+ | >80″ | Specialized infrastructure (dams, flood control, nuclear power plants) | Harvinainen, highly customized; extremely high torque; usually metal-seated for durability |
Common Pressure Classes and Equivalence
Butterfly valves are produced in both metric PN classes ja imperial ANSI classes.
| PN Class (Metri-) | ANSI / ASME Class (Keisarillinen) | Typical Working Pressure (20 ° C) | Yleiset sovellukset |
| PN6 | Luokka 125 | 6 baari / 87 psi | Low-pressure water supply, LVI, light-duty service |
| Pn10 | Luokka 150 | 10 baari / 145 psi | General water treatment, irrigation, ruoka & juoma |
| PN16 | Luokka 150 | 16 baari / 232 psi | Municipal pipelines, fire protection, öljy & gas distribution |
| PN25 | Luokka 300 | 25 baari / 363 psi | Chemical process plants, medium-pressure steam, industrial gas |
| PN40 | Class 300–600 | 40 baari / 580 psi | Korkeapaineinen höyry, petrochemical units, sähköntuotanto |
| PN63+ | Class 600–900+ | >63 baari / >913 psi | Critical service, jalostamot, nuclear and high-pressure process systems |
Face-to-Face and Actuator Mounting Standards
Lug butterfly valves follow international dimensional and mounting standards to ensure interchangeability:
- Face-to-face dimensions: Typically conform to ISO 5752 sarja (short, medium, or long pattern).
This ensures that valves of the same size and series can be interchanged regardless of manufacturer. - Actuator mounting interface: Määritelty jstk ISO 5211, which standardizes bolt-hole patterns, drive shafts, and mounting pads for part-turn actuators (manual gear, pneumaattinen, sähköinen, tai hydraulinen).
End Connections and Flange Compatibility
Se lug-type design uses threaded bosses (lugs) that align with flange bolt holes, allowing independent bolting to each side of the valve.
This provides advantages for pipeline disassembly and end-of-line service.
| End Connection Type | Mounting Method | Piirteet | Tyypillinen käyttö |
| Lug | Threaded lugs bolted to pipe flanges | Allows one-side disassembly; end-of-line capability | Vettä, LVI, medium-pressure pipelines |
| Vohveli | Sandwiched between two flanges with through-bolts | Kevyt, taloudellinen | Low-pressure service, tight spaces |
| Flanged | Integral cast flanges bolted to pipe flanges | Vahvempi, suitable for higher pressure | Power plants, heavy-duty process industries |
6. Core Performance Metrics of Lug Butterfly Valve
| Metri- | Määritelmä | Tyypilliset arvot (6-inch Lug Butterfly Valve) | Engineering Implications |
| Virtauskerroin (Cv) | Flow capacity: US gallons of water per minute (GPM) at 60 °F with 1 psi paineen lasku. | • Concentric (EPDM seat): 200–230• Double Eccentric (metal seat): 160–190• Triple Eccentric (metal seat): 150–180 | Higher Cv = lower pumping energy. For throttling, double/triple eccentric valves provide more stable flow control. |
| Paineen pudotus (ΔP) | Energy loss across the valve at nominal flow. | <3 psi at 500 GPM (6-inch concentric valve) | Low ΔP reduces system operating cost; eccentric designs slightly higher but improve shutoff capability. |
| Operating Torque | Torque required to rotate the disc fully open/closed under design pressure. | • Concentric: 60–100 N·m• Double Eccentric: 120–180 N·m• Triple Eccentric: 150–220 N·m | Critical for actuator sizing. Under-sizing actuator may cause failure in high ΔP or emergency shutoff. |
Vuotoluokka |
Defines allowable leakage per API 609 / ISO 5208. | • Class IV (0.01% of rated flow)• Class VI (bubble-tight, ~0.00001%) | Elastomer seats achieve Class VI; metal seats usually Class IV–V but withstand higher temperatures. |
| Cycle Life | Expected open/close cycles before major seat replacement. | • EPDM seat: ~10,000 cycles• PTFE seat: ~25,000 cycles• Metal seat: 50,000–80,000 cycles | Determines maintenance interval. Metal-seated valves preferred in high-cycle or abrasive service. |
7. Applications of Lug Butterfly Valve
- Vettä & wastewater — pump isolation, PRV bypass, large DN gate replacements. (Typical DN: 50-2000)
- LVI / building services — balancing, isolation and fire dampers.
- Öljy & kaasu / petrokemian — low to medium pressure isolation; when higher integrity required use metal-seat eccentric types.
- Kemiallinen prosessointi — PTFE lined lug valves for corrosive media.
- Power generation — cooling water, feed systems, auxiliary systems (resistant materials and testing required).
- Meren — seawater service, overboard discharge (bronze/duplex materials).
- Fire protection — lug style is commonly used because it can be installed between flanges and used as an end-of-line device.
- Ruoka & lääke — sanitary butterfly valves (special finishes, FDA-compatible seats).
8. Edut & Limitations of Lug Butterfly Valves
Key Advantages of Lug Butterfly Valves
- Maintenance Efficiency: Lug design reduces valve replacement downtime by 70% vs.. wafer valves (4–6 hours saved for a 12-inch line).
- Kustannustehokas: 30% lower cost than flanged valves; 20% higher pressure rating than wafer valves.
- Bidirectional Flow: No flow direction restriction—ideal for backwashing, reverse flow, or bi-directional process lines.
- Matala paineen pudotus: ΔP <3 psi at nominal flow—reduces pump energy use by 5–8% vs. palloventtiilit.
- Monipuolinen: Handles liquids, kaasut, ja lietteet (with metal seats) across temperatures from -196°C to 482°C.
Limitations of Lug Butterfly Valves
- High-Pressure Cap: Max ANSI Class 900 (210 baari)—unsuitable for ultra-high-pressure service (>210 baari; use ball valves).
- Abrasive Media Risk: Pehmeät istuimet (EPDM/PTFE) wear quickly in slurries (life <1,000 cycles vs. 10,000+ for non-abrasive service).
- Throttling Accuracy: Concentric designs have non-linear flow vs. angle—inferior to globe valves for precision dosing (ESIM., kemiallinen injektio).
- Paino: 30–50% heavier than wafer valves—not ideal for weight-sensitive applications (ESIM., ilmailu-).
9. Comparison with Other Valves
Lug butterfly valves are widely considered a mid-range solution between compact wafer valves and heavier-duty gate or ball valves.
Their unique bolted-lug design provides ease of installation and maintenance, but performance trade-offs exist when compared with other valve families.
| Kriteerit | Lug Butterfly Valve | Wafer Butterfly Valve | Palloventtiili | Porttiventtiili | Maapalloventtiili |
| Rakenne & Toiminta | Neljännesvuoro, disc with lugs bolted to flanges | Neljännesvuoro, disc clamped between flanges | Neljännesvuoro, spherical closure | Linear motion, sliding wedge | Linear motion, perpendicular disc |
| Kokoalue (Inches) | 2–48 | 2–48 | ½–24 | 2–60 | 2–36 |
| Flow Characteristics | Moderate Cv, good throttling (eccentric types) | Similar Cv, less rigid, more prone to leakage | Very high Cv, near full-bore flow | Full bore, minimal ΔP when open | Precise flow control, higher ΔP |
| Paineen pudotus (ΔP) | Matala – kohtalainen (0.5–3 psi for 6-inch at nominal flow) | Matala – kohtalainen | Minimaalinen | Minimaalinen | Kohtuullinen - korkea |
| Pressure / Temperature Capability | Class 150–900, up to ~482 °C (metal seat) | Class 150–300, low-to-medium temperature | Class 150–2500, up to ~650 °C | Very high pressure/temperature | High pressure, high temperature |
| Installation & Huolto | Easy inline removal; allows blind flange on one side | Requires unbolting both flanges for removal | Robust sealing; isompi, heavier actuators | Difficult maintenance; large footprint | Requires more space, higher torque |
| Kustannustaso | Keskipitkä | Matala | Korkea | Korkea | Korkea |
| Tyypilliset sovellukset | Vettä, LVI, kemikaali-, fire protection | Low-pressure, space-limited pipelines | Öljy & kaasu, korkeapaineinen eristys | Water mains, höyryä, jalostamo | Power plants, dosing, control loops |
10. Johtopäätös
Lug butterfly venttiilit offer a versatile, luotettava, and easy-to-maintain solution for industrial fluid control.
Their lug design simplifies installation, eccentric or concentric discs ensure tight sealing, and diverse material options handle a wide range of media and temperatures.
Widely used across water treatment, LVI, kemikaali-, ja öljyä & gas sectors, they balance performance, kestävyys, ja kustannustehokkuus.
Heidän suunnittelunsa ymmärtäminen, materiaalit, and performance characteristics is key to optimizing flow control, minimizing downtime, and ensuring operational safety.
Faqit
Can lug butterfly valves be used for gas service?
Yes—double eccentric lug valves with PTFE or metal seats (API 609 Class VI leakage) are suitable for gas service (ESIM., maakaasu, typpi).
Ensure compliance with ISO 15848-1 Class AH for low fugitive emissions (<1×10⁻⁹ Pa·m³/s).
What is the maximum temperature a lug butterfly valve can handle?
Metal-seated double eccentric valves (316L SS body, Stellite® seat) handle up to 650°C—suitable for high-temperature steam or gas service.
Elastomeric seats (EPDM) are limited to 150°C.
How do I prevent stem leakage in corrosive environments?
Use 316L SS stems with PTFE or FFKM packing; apply a passivation coating to the stem; and inspect packing quarterly for wear. For critical service, use bellows seals (zero leakage).
Q4: Are lug butterfly valves suitable for fire protection systems?
Yes—select ductile iron/carbon steel body, EPDM seat (fire-rated per UL 10C), ANSI Class 150, and manual gear actuator. Ensure compliance with NFPA 13 (fire sprinkler systems).
What is the difference between single and double eccentric lug valves?
Single eccentric valves offset the disc center (vähentää kitkaa, ANSI Class 300–600).
Double eccentric valves offset both disc and stem (eliminates seat contact until closure, ANSI Class 600–900, Class VI leakage)—ideal for high-pressure/gas service.
