Butterfly Valve

Written by Jerry Ratzlaff. Posted in Valve

A butterfly valve is a quarter turn valve (90° or less) with a circular disk as its closing element. The standard design has the valve stem running through the disk, giving a symmetrical appearance.  Other designs offset the stem. Advantages include less wear and tear on the disk and seats, and tighter shut-off capabilities.  When space is limited, sometimes larger valves may use a hand wheel with a gear arrangement.  Butterfly valves are rather easy to maintain.  These valves are used for gases, liquids, slurries, powders, and vacuum.  

  • There are two butterfly valve categories:
    • Category A: Manufacturer's rated cold working pressure (CWP) butterfly valves, usually with a concentric disc and seat configuration.  Sizes covered are NPS 2 to NPS 48 for valves having ASME Class 125 or Class 150 flange bolting patterns.
    • Category B: Pressure-temperature rated butterfly valves that have an offset seat and either an eccentric or a concentric disc configuration.  These valves may have a seat rating less than the body rating.  Sizes covered are NPS 3 to NPS 24 for Classes 150, 300, and 600.

Abbreviations

  • BTFLV - butterfly valve

butterfly valve Characteristics

High Performance Butterfly Valve

Techinically a  High Performance Butterfly Valves (HPBV) is not a butterfly valve.  However, for intents and purposes, its function and dimensions are equivalent to butterfly valves.  A HPVB must meet certain criteria.  For a butterfly valve to be determined as high performance it must:

  • Provide bubble tight shutoff for the entire range of its rated ANSI differential pressure across the valve.
  • Be bidirectional in nature

Typically, HPBV will be of a double or triple offset design.

Lug Style Butterfly Valve

Lug butterfly valves connect directly to the flanges by means of a lug or machine bolt.  Since these are attached directly to the flanges, each length of pipe on either side of hte valve can be removed and replaced independant of the other.

Unlike a wafer type butterfly valve, a lug style valve can serve as an end of the line valve

Some lug types are threaded such that two machine bolts are needed to install the valve.  Some have the threads drilled out through the body.  If the threads are drilled out through the body, avoid specifying a single bolt to thread all the way through the body.  This is because the installer must then thread the bolt through the valve THEN install the nut on the end.  This more labor intensive than installing a single machine bolt on each side of the valve.

Lug style butterfly valves have the same face to face dimensions as a wafer style butterfly valve.

Wafer Style Butterfly Valve

A wafer style butterfly valve is a valve that is sandwiched between two flanges.  When installed, the bolts that hold the two flanges together hold the valve in place.  When designing when uing a wafer style butterfly valve, the bolt lengths need to be adjusted to include the thickness of the valve and the added gasket.  While wafer type valves don't have attachment lugs, they may have lugs that help align them between the two flanges.

Wafer style butterfly valves are generally cheaper than lug style butterfly valves.  This is because there are less materials and less machining is needed to make a wafer style butterfly valve.

Wafer style butterfly valves have the same face to face dimension as a lug style butterfly valve.

Flange Style Butterfly Valve

A flange style butterfly valve is a butterfly valve with a flange on each end.  These have a larger face to face dimension than the wafer and lug style butterfly valves and should not be used when there is limited space. 

Fire Tight Valve

When using valves in a service that may provide fuel to a fire, it is important to ensure that they are "fire tight."  Typically the seat in a soft seated fire tight valve contains a metal strip that will provide additional sealing should the seat be burnt or melted away.  Fire tight valves can be found on fuel gas applications, VRU systems and in other flammable systems.

Butterfly Valve Datasheets

Face to face dimensions for full and standard port valves is the same.  All ball valves 2" and below are both standard and full port valves.

data lug butterfly valve 1    

standards

API Standards

  • API Std 598 - Valve Inspection and Test
  • API Std 609 - Butterfly Valves: Double-Flanged, Lug- and Wafer-Type

ASME Standards

  • ASME B1.1 - Unified Inch Screw Threads, (UN and UNR Thread Form)
  • ASME B16.1 - Gray Iron Pipe Flanges and Flanged Fittings: Classes 25, 125, and 250
  • ASME B16.5 - Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24 Metric/Inch Standard
  • ASME B16.20 - Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed
  • ASME B16.24 - Cast Copper Alloy Pipe Flanges and Flanged Fittings: Classes 150, 300, 600, 900, 1500 and 2500
  • ASME B16.34 - Valves Flanged, Threaded and Welding End
  • ASME B16.42 - Malleable Iron Threaded Pipe Unions: Classes 150, 250, and 300
  • ASME B16.47 - Large Diameter Steel Flanges: NPS 26 Through NPS 60 Metric/Inch Standard
  • ASME B31.3 - Process Piping
  • ASME B46.1 - Surface Texture (Surface Roundness, Waviness, and Lay)

AWWA Standards

  • AWWA C504 - Rubber Seated Butterfly Valves
  • AWWA M49 - Butterfly Valves: Torque, Head Loss & Cavitation Analysis

BSI Standards

  • BS 5155 - Specification for butterfly valves

ISO Standards

  • ISO 5752 - Metal valves for use in flanged pipe systems -- Face-to-face and centre-to-face dimensions
  • ISO 10631 - Metallic butterfly valves for general purposes

MSS Standards

  • MSS SP-6 - Standard Finishes for Contact Faces of Pipe Flanges and Connecting-End Flanges of Valves and Fittings
  • MSS SP-25 - Standard Marking Systems for Valves, Fittings, Flanges and Unions
  • MSS SP-44 - Steel Pipeline Flanges
  • MSS SP-45 - Bypass and Drain Connections
  • MSS SP-67 - Butterfly Valves
  • MSS SP-91 - Guidelines for Manual Operation of Valves

Butterfly Valve Photos