Butterfly valve

The shut-off valve is a valve for controlling the flow of a fluid in a pipeline. In this design, the flow is changed by a rotating disc in the flow cross-section. When the flap is fully open, the disc is aligned parallel to the flow direction. The rotation of the disc occurs at smaller sizes by one to be operated by hand lever, in larger diameters by a hand crank with gear. An actuator driven by a drive motor or a hydraulic or pneumatic drive is also possible. They are well suited for restricting fluid flow ( throttle valve ), but have also in the fully open state, a certain flow resistance. Your floor space in the pipeline is very low. The Zwischenflanschbauart that can be clamped between two flanges has a low overall length. Depending on the fluid are very large torques of tens of thousands Newton meter (Nm) to spend.

Types of Butterfly Valves

There are four kinds of butterfly valves essentially:

  • Centric design ( pivot point is in the middle of the seat and in the center of the pipe )
  • Simply eccentric, in which the disc rotation out of the plane of the seat, is located along the pipeline axis, moved (ball segment valves)
  • Double eccentric, in which the pivot point is not located in addition in the middle of the pipe (for example any standard door is a double eccentric butterfly valve. )
  • Triple eccentric butterfly valve (also the axis of rotation of the seat is non-parallel and non- symmetrically with respect to the pipe axis ).

Depending on the design are different sealing materials used:

  • Elastomer or polymer (eg PTFE) ( Resilient Seated Butterfly Valve)
  • Metal ( metal seated butterfly valves )

While the cheapest method of construction of the centric butterfly valve can only be produced with soft-sealing gaskets, the triple eccentric flap reaches the absolute freedom from friction and can reach very high lifetime in large diameters (switching cycle numbers to 250,000 cycles at full function) with metallic seals.

Resilient Seated Butterfly Valves are designed bar in sizes of up to several meters and low nominal pressures, usually up to a maximum of 16 and a maximum for temperatures up to 200 ° C suitable. The seals are performed, as a rule as a case liner made ​​of elastomer, here is the maximum possible temperature to 150 ° C or PTFE. The sensitivity of a soft-seal flap to contamination is also low. However, even small leaks due to the large sitting cross-section lead to significant leakage quantities. Another problem is the sealing of the rotary axis with respect to the environment. Here leaks can not be avoided quite often.

Metal Seated Butterfly Valves are designed bar in nominal widths of up to two meters and pressure ratings up to 200. The main advantage is the extremely good usability at very low and very high temperatures. Temperatures from -200 ° C to 1100 ° C Cryogenic use or, for example, exhaust valves in submarines are common applications. Leakages can be entirely eliminated even by vacuum applications. Seals the shaft by means Stopfpackung make the fittings absolutely tight even with media such as helium or hydrogen. In contrast, metal-seated valves are relatively sensitive to solids in the medium.

For increasing the tightness with large dimensions Doppelabsperrklappen can be used. This consists of two valve discs, which are operated in parallel, a space which is acted upon by a barrier medium (air or liquid).

A special design of the butterfly valve is the check valve.

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