What is a butterfly valve? | ACI Industriearmaturen GmbH

Butterfly valves

Applications / Body types / Functional designs / Seals

Butterfly valves usually consist of a compact housing, the disc for shutting off or releasing the flow, a shaft (with bearings and seals) and the actuating element. The actuating element is used to open or close the valve disc by a 90° rotary movement. When the valve is fully open, the disc is parallel to the direction of flow, in the medium flow.

The classic field of application of butterfly valves:

Butterfly valves are usually used purely as shut-off valves for on/off operation. Since the valve disc is in the flow path even when fully open, it is not recommended for use with media containing solids. A full, free passage is therefore not given here. This means that cleaning of the pipeline, e.g. by pigs, is not possible.

Butterfly valves are also suitable to a certain extent for throttling or regulating the flow medium, although they have the following disadvantage due to their design. The further the valve disc is closed, the more the flow velocity increases in the passage. This causes cavitation and water turbulence, which can damage the internal components, especially the seals.

The installation position of the butterfly valve is variable as long as the valve shaft is horizontal.

Butterfly-valve-centric-soft-sealed-cross-section

Butterfly valve, centric 

Butterfly-valve-centric-soft-sealing

Butterfly valve with tapped eyes


They are operated manually via a hand lever or, in the case of larger nominal sizes, via a gearbox with handwheel. Automated butterfly valves can be operated via electric actuators, pneumatic or hydraulic actuators.

The advantages of butterfly valves over valves, gate valves and ball valves are their simple design and compact dimensions. They require less material, are lighter in weight and require less space for installation, resulting in significant cost savings. They are very versatile and have a very short actuation time due to the 90° rotation.

The design-related arrangement of the valve disc, which is located in the flow path, has a disadvantage. Therefore, they are rather unsuitable for media containing solids and the pipeline is not piggable. Due to the flow resistance of the disc when fully open and the increased flow velocity when closing, damage can occur inside and the sealing properties can be negatively affected.

Classification of butterfly valves based on the following characteristics:

  • Body shape: Wafer, flanged or flanged design
  • Functional design: Centric or eccentric butterfly valves
  • Sealing type: Soft sealing or metal sealing

Body shapes

Butterfly-valve-wafer-type

Butterfly valve, wafer type,
centric, soft-seated

Wafer type design

Wafer type butterfly valves consist only of an annular body with the disc installed, the sealing element, the shaft with bearings/seals, and the structure for the actuating element. They are simply clamped between two line flanges, which is why they are also called clamp-in valves. There are usually four centering eyes on the body, which can be used to fix the valve between the flanges in the desired installation position.

Due to their light and simple design, the amount of material used is very low, which is why they are the most inexpensive butterfly valves.

Lug type design

known as tapped eyes) so that the valve can be bolted directly to the mating flanges. This has the advantage that the pipeline can be dismantled on one side: the butterfly valve can be used as a so-called end fitting.

Butterfly-valve-lug-type

Butterfly valve, lug type,
centric, soft-seated

Butterfly-valve-double-flanged-design

Butterfly valve, double-flanged type,
centric, soft-seated

Double-flanged design

The valve body has an integrated U-profile flange on both sides and also offers the advantage of a short overall length and the associated savings in material, weight and manufacturing costs.

Flanged butterfly valves

Flanged butterfly valves have a flanged connection on both sides and were developed as a low-cost alternative to wedge gate valves. They have the same short face-to-face length according to EN 558-1 basic series 14, but are less expensive to manufacture and much easier to install due to their compact design and lower material usage. The larger the nominal size, the more noticeable the price difference.

Butterfly-valve-flanged-design

Butterfly valve, flanged type,
centric, soft-seated

Functional designs

Butterfly-valve-centric-soft-sealed-cross-section

Butterfly valve,
centric, soft-seated

Centric butterfly valves

They are the "original type" of wafer butterfly valves and are still the most commonly used valve design today. They are usually soft-seated and bi-directional, i.e. seal on both sides. When closed, the disc "sits" in the surrounding annular bellows, the sleeve, and thus seals.

Centric means that the disc is rotated 90° around its own axis to open or close. The shaft is located in the center of the disc, so the center of rotation is in the center of the disc seat and thus in the center of the pipeline.

Eccentric butterfly valves (single, double and triple eccentric)

In a single eccentric butterfly valve, the pivot point of the disc (1)  is slightly displaced from the seating plane along the pipe axis. This reduces the operating forces of the butterfly valve and wear.

Double eccentric means that, in addition to this, the pivot point of the valve disc (2) is no longer located in the center of the pipe. This design offers the following advantages:

  • The actuating torques are lower than with centric butterfly valves, which is particularly noticeable with larger nominal sizes and higher operating pressures.

  • The inflow is much more favorable than with shut-off bodies perpendicular to the pipeline, which reduces wear.

  • The stress on the sealing elements is reduced, which also reduces wear and reduces maintenance requirements.

Butterfly-valve-double-eccentric-cross-section

Double eccentric butterfly valve,
metal-seated

A butterfly valve is triple eccentric if the rotation axis of the seat (3) is also not parallel and not symmetrical to the pipeline axis. This means in detail:

  • Eccentricity 1: The damper shaft is located behind the seat plane.

  • Eccentricity 2: The damper shaft is offset on one side to the center axis of the pipeline.

  • Eccentricity 3: It is achieved by an inclined, conical profile of the seat. As a result contact between the sealing surfaces of the disc and the body occurs only at the body only at the last moment.

Butterfly-valve-triple-eccentric-cross-section

Triple eccentric butterfly valve,
metal-seated

This triple eccentricity means that the 90° rotation of the valve disc to open or close the valve is almost frictionless and prevents the disc from jamming.

The actuating forces and also the wear are considerably minimized and the service life is extended many times over.

Two-way (bidirectional) flow through the butterfly valve is possible, with the medium assisting either the opening or closing of the disc, depending on the direction of flow.

Another advantage is the virtually leak-free tightness that can be achieved with triple-eccentric butterfly valves. This also allows vacuum applications or use at high operating pressures, high or very low operating temperatures. They can even be used for extreme temperature fluctuations and pressure peaks.

Types of seals

Soft-seated butterfly valves

The classic butterfly valves have a soft-seated design and are suitable for low to medium operating pressures up to 16 bar. Depending on the sealing material, they are suitable for operating temperatures up to a maximum of +200°C. They are manufactured from nominal size DN 25 to over DN 2000.

The sealing element, the sleeve, is vulcanized onto very low-cost models as a body liner and cannot be replaced if damaged and/or worn. Most manufacturers nowadays offer the sleeve as a maintenance-friendly spare part for replacement.


Butterfly-valve-soft-seated

Butterfly valve, soft-seated

Commercially available sealing materials are:

  • NBR (Nitrile Butadiene Rubber):
    Good resistance to mineral oils, greases, water, gases, hydrocarbons or oils. Temperature range: -10°C to +80°

  • EPDM (Ethylene Propylene Diene Monomer):
    Good resistance to heat, drinking / hot water or chemicals. Temperature range: -10°C to +130°C

  • FKM / FPM (Fluorocarbon rubber) (Viton®):
    High thermal and chemical resistance, suitable for oils, chemicals or other media. Temperature range: 0°C to +150°C

  • PTFE (Polytetrafluoroethylene) (Teflon®):
    Good resistance to chemicals, aggressive and corrosive media, acids, chlorine, etc. Temperature range: -30°C to +200°C

Metal-seated-butterfly-valve

Butterfly valve, metal-seated

Metal-seated butterfly valves

These butterfly valves are manufactured up to nominal size DN 2000 and are suitable for operating pressures up to 200 bar. They are very suitable for extreme temperature conditions: depending on the material combination from -200°C up to +1100°C, for high temperature applications.

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