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Valve Design Features of Triple Offset, Metal-Seated Butterfly Valves
　


Triple offset butterfly valve, this advanced design features three-way eccentricity and unique elliptical seat geometry ensuring compressive sealing around entire seat and a “tight” bubble free valve.

Internal
 External
DOUBLE SHAFT BLOWOUT PROTECTION
CONFORMS TO API 609
 
  • SEAT


    Raised, conical seat prevents solids build-up from interfering with seal. Seat is hardfaced with Stellite to meet severe service. Alternative space age alloys are also used.
  • LAMINATED RESILIENT DISC SEAL to 1000oF (538oC) One to four graphite layers are carefully assembled between stainless steel rings using Phenolic Resin. Flexible seal rings without glue are available for higher temperatures.
  • "ZERO LEAKAGE" - SEAT TIGHTNESS
    The disc seal, evenly compressed around its circumference, produces a wedging effect which flexes the seal ring and reacts like a spring. The resilient seal assures "zero leakage" of liquids or gases to API 598 - resilient seat standard. Resiliency in the seal allows disc movement during thermal cycles while retaining tight shutoff as shown.
  • NO CAVITY
    There is no cavity (contrary to gate valves) to allow build-up of solids.
  • ONE-PIECE SHAFT
    Large diameter shaft for safety is connected to the disc close to the bearings to absorb loads with taper pin and key to allow for differential expansion due to temperature.
  • SHAFT BEARINGS
    The shaft is centered on two long bearings, chromed, nitrided, or as stellite (option) protected against the entrance of solids by O-rings (Bearing flush taps available as an option).
  • LOW EMISSION SHAFT SEALS 0–20 ppm
    Shaft is burnished to 8 RMS, ID of packing chamber finish 32 RMS. Live-loading available for long maintenance free service. Easy access for packing adjustment.

From: NVF valve knowledge

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