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Vridspjällsventil/Butterfly Valve

Butterfly Valves

A butterfly valve is a quarter-turn rotational motion valve, that is used to stop,
regulate, and start flow.
Butterfly valves are easy and fast to open.
A 90° rotation of the handle provides a complete closure or opening of the valve.
Large Butterfly valves are usually equipped with a gearbox, where the
handwheel by gears is connected to the sterm.
This simplifies the operation of the valve, but at the expense of speed.

Advantages of butterfly valves
• Compact design requires considerably less space, compared to other valves
• Light in weight
• Quick operation requires less time to open or close
• Available in very large sizes
• Low-pressure drop and high-pressure recovery

Disadvantages of butterfly valves
• Throttling service is limited to low differential pressure
• Cavitation and choked flow are two potential concerns
• Disc movement Is unguided and affected by flow turbulence
Image of a typical Butterfly valve, Lug Wafer type design.

Types of Butterfly Valves
Butterfly valves has a short circular body, a round disc, metal-to-metal or
soft seats, top and bottom shaft bearings, and a stuffing box.
The construction of a butterfly valve body varies.
A commonly used design is the wafer type that fits between two flanges.
Another type, the lug wafer design, is held in place between two flanges by
bolts that join the two flanges and pass through holes in the valve's outer
casing.
Butterfly valves are even available with flanged, threaded and butt welding ends,
but they are not often applied.
Some applications with sea water and butyl lined butterfly valves can be
flanged with the purpose for the butyl liner. So it doesn´t brake the butyl liner inside
the pipeline when fully open.

Seat Disk and Stem of a Butterfly Valve
Stopping flow is achieved by the valve disk sealing against a seat that is on
the inside diameter periphery of the valve body.
Often an elastomeric seat material will be used.
Disk and stem of a butterfly valve consists of two parts, and there a two
methods to be fastened together.
In the first method, the disk is bored through and secured to the stem with
bolts or pins.
The second method involves boring the disk as before, then shaping the
upper stem bore to fit a squared or hex-shaped stem.
This method allows the disk to "float" and seek its center in the seat.

Typical Applications of Butterfly Valves
A butterfly valve can be used in many different fluid services and they perform
well in slurry applications.
The following are some typical applications of butterfly valves:
• Cooling water, waste water, air, gases, fire protection, fuel oil, et cetera
• Slurry and similar services
• Vacuum service
• High-pressure and high-temperature water and steam services
(called High Performance Butterfly valves)
The following are some typical applications of High Performance
Butterfly valves:
• Petroleum, gas, chemical & petrochemical industry
• Nuclear power stations, sugar industry, paper industry
• Geothermal energy, shipbuilding, low pressure steam
• Vacumm service

Resilient type will have soft seats, high performance is usually
double eccentric and tricentric are usually with metal seats.

The varying designs allow for tight shut-off or throttling service.
Available in sizes: 2” to 36” in ANSI Class 150LB to 2500LB
Design: API 609, BS 5155, MSS-SP-67 and firesafe to
API 607 where applicable
Ends: Designed to suit either Flat face, RF or RTJ Flanges
Materials: WCB, LCB, CF8, CF8M
Trims: Stainless Steel, 17.4PH with Seats PTFE, RPTFE,
Metal or Rubber

Special materials also available:
Duplex, Super Duplex, Monel, Hastelloy, Titanium, Inconel, Incoloy, 6MO

Modifications include Gearbox, Actuation and Stem Extensions.

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