Pin vs Pinless Butterfly Valves Key Differences in Stem-to-Disc Connection

Butterfly valves stay vital in pipeline setups for managing fluids. The main split between pin-type and pinless butterfly valves comes from the way the stem links to the disc.

· Pin-type butterfly valves secure the stem and disc with metal pins (cylindrical or conical).

· Pinless butterfly valves achieve direct connection through specialized stem shapes (square, hexagonal, or D-shaped) mated to precision-machined disc hubs, eliminating separate pins.

This setup gap affects price, dependability, leak-proofing, and fit for jobs. FLUIDO, a top butterfly valve manufacturer and supplier since 1994, builds both kinds in its ISO9001-approved plants in Shandong and Hebei. It serves more than 400 buyers worldwide in over 35 nations.

1. Pin-Type Butterfly Valve

Connection Principle

The stem has pin slots at its bottom end. The disc has slots that match. One or two metal pins slide through these slots. They pass turning force from the stem's spin to the disc's shift.

Core Characteristics

· Simple Structure: Mature design with low machining complexity enables cost-effective production.

· Cost Advantage: Manufacturing costs run 15%-30% lower than pinless designs, ideal for high-volume procurement.

· Assembly-Dependent Reliability: Pin strength, fit tolerance, and anti-loosening measures (split pins, sleeves) determine service life. High-frequency cycling or large torque can cause wear, loosening, or pin shear.

· Low Machining Difficulty: Standard machine tools suffice for pin-hole drilling; suitable for small to mid-size manufacturers.

· Easy Spare Parts Sourcing: Pins follow standards like GB/T 119; replacements ship quickly without custom fabrication.

· Moderate Maintenance: Pin failure requires valve disassembly and replacement—time-consuming but straightforward.

Core Drawbacks

· Weak Link Exposure: Pins bear concentrated shear and torque; prolonged operation enlarges pin holes, causing backlash and erratic actuation.

· Higher Leakage Risk: Pin holes in the disc create potential leak paths, especially under corrosive media or high pressure.

· Torque Limitations: Large diameters (DN≥600) or pressures (PN≥16) demand oversized pins, increasing weight and reducing reliability compared to pinless alternatives.

Typical Applications

· Low-Pressure Ambient Systems: Municipal water supply, HVAC chilled water loops (≤PN10, -20°C to 120°C).

· General Industrial Fluids: Power plant cooling circuits, non-corrosive wastewater, compressed air isolation.

· Cost-Sensitive Projects: Urban pipeline retrofits, small-scale factory distribution networks prioritizing economy.

2. Pinless Butterfly Valve

Connection Principle

The stem ends in a flat-sided shape (square, hex, or D-form). The disc hub gets a finely drilled match space. Tight press fit, weld join, or lock tools like snap rings or screws make a stiff turn pass. No loose bits are used.

Core Characteristics

· Compact & High-Strength: Eliminates pin shear points; torque transfers directly, boosting torsional capacity by over 30%.

· Superior Sealing: No through-holes in the disc minimize leak paths; pairs seamlessly with PTFE or metal seats to achieve ANSI Class VI shutoff.

· Extended Service Life: Resists wear under daily cycling; lifespan 2–3× longer than pin-type in aggressive duty.

· Higher Cost: Micron-level tolerances (e.g., ±0.01 mm) require CNC machining centers, elevating production expense.

· Integrated Strength: Direct stem-to-disc interface handles large torque without fatigue failure.

· Reliable Sealing Performance: Complete disc integrity supports zero-leakage designs for hazardous fluids.

Core Drawbacks

· Elevated Cost: Precision stem profiling and disc boring demand advanced equipment; unit price exceeds pin-type valves.

· Complex Repair: Damage to the interference zone typically requires stem-and-disc replacement as an assembly.

· Limited Interchangeability: Proprietary geometries prevent cross-brand part swapping; spares must come from the original manufacturer (e.g., FLUIDO).

Typical Applications

· Strong-Push Pipes: Oil plant process lines (PN16–PN40), gas send lines.

· Eating or Risky Stuff: Acids, bases, chlorine gas, fire-start solvents that need firm close.

· Big-Size & Fast-Turn Jobs: Waste plant pump outs (DN800–DN2000), steel coal-gas paths.

· Key Trust Setups: Nuclear side cooling, drug clean water loops that need steady run.

Material Selection Impact on Pin vs Pinless Performance

Body & Disc Materials

· Cast Iron (GG25) + EPDM: Pin-type leads in water/HVAC (≤120°C).

· Ductile Iron (GJS-500-7) + Nylon Coating: Pinless picks for rough water with sand bits.

· Carbon Steel (WCB) + RTFE: Pinless key for steam to 250°C.

· Stainless Steel (CF8M) + Metal Seat: Pinless must for LNG, chlorine, or Class VI close.

Stem Material & Coating

· 410SS + Hard Chrome: Usual for pin-type.

· 17-4PH + Stellite Facing: Pinless for fast-turn uses (>50,000 cycles).

FLUIDO Material Traceability: EN 10204 3.1 certificates, PMI testing, and third-party checks (SGS/BV) lock in rules.

FAQ

Q1: What is the main visual difference between pin and pinless butterfly valves? A: Pin-type valves show a clear taper pin or bump on the disc at the stem link. Pinless ones look even without outer pins or slots.

Q2: Why might a pin-type butterfly valve develop leaks over time? A: Fluid can slip through pin slots into the gap between disc and stem. This sparks rust, pin snaps, or inside leaks.

Q3: Which design is easier to maintain and repair in the field? A: Pinless valves break down simpler without pushing pins out. Stem and disc swaps go quicker.

Q4: Are pinless butterfly valves suitable for high-pressure applications? A: Yes, mainly in low to mid push (up to PN16). For wild forces, check fine cuts to skip wear on join faces. Pin-type gives better start hold.

Q5: How does the pinless design impact operating torque? A: Pinless valves, mainly with nylon-coated discs, cut turn needs by up to 40% over pin-type. This comes from self-slick and smooth turn pass.

Q6: What are the risks of fatigue failure in pin-type valves? A: Long turns can crack pins from side stress. This shifts the disc or breaks valve work. Pinless skips this with straight tight fits.

Contact FLUIDO – Your Trusted Butterfly Valve Manufacturer & Supplier

Engineering firms, EPC contractors, and system integrators seeking reliable pin-type or pinless butterfly valves partner with FLUIDO for:

· Competitive OEM pricing and MOQ flexibility

· Fast lead times (stock for standard sizes; 4–6 weeks for custom)

· Complete documentation package and global logistics support

Request a quotation today at info@fluidovalve.com.