In brief
A butterfly valve is a pipeline valve that opens or shuts off the flow with a rotatable disc by means of a quarter turn.
Contents
What is Butterfly valve?
The butterfly valve belongs to the quarter-turn valves: a disc sits on a shaft in the middle of the flow path and is rotated through 90 degrees between the open and closed positions. Compared with gate valves or ball valves, it is short, light and inexpensive in large nominal sizes. It is used in water, wastewater, cooling and process lines, sometimes also for coarse throttling.
A distinction is made between concentric valves with a soft-sealing elastomer liner and double and triple offset valves, which handle higher pressures and temperatures and can also be metal-seated. For installation, there are wafer versions, lug versions with threaded lugs that are also suitable as end-of-line valves, and double-flanged valves. Important parameters are nominal size (DN), nominal pressure (PN), face-to-face dimension, materials of the body, disc and liner, and operation by hand lever, gearbox or valve actuator.
Typical causes of failure are worn or swollen liners, deposits on the disc, cavitation during continuous throttling and leaking shaft passages. The valve can often be repaired by replacing the liner or shaft seals, provided these are available as spare parts.
In practice: maintenance and procurement
A spare parts enquiry requires the nominal size, nominal pressure, design (concentric or offset), installation type, materials, medium and temperature, as well as the actuator connection. A photo of the nameplate and the flange connection often saves several follow-up questions.
Synonyms and abbreviations: wafer butterfly valve · lug butterfly valve · throttle valve · high-performance butterfly valve
Frequently asked questions
What is the difference between a butterfly valve and a ball valve?
Both valves are operated with a quarter turn. In the open position, a ball valve usually provides an almost unobstructed passage and seals very reliably, but it is heavy and expensive in large nominal sizes. The butterfly valve is shorter and lighter, but the disc remains in the flow path even in the open position and causes a certain pressure loss.
What do concentric and offset mean for butterfly valves?
In a concentric valve, the shaft is centred in the disc and seal, and the disc seals against an elastomer liner. In offset (eccentric) valves, the shaft is positioned off-centre so that the disc lifts quickly away from the sealing surface when opening. This reduces friction and wear and allows higher pressures and temperatures as well as metal seals.
What information is needed to replace a butterfly valve?
Required are the nominal size, nominal pressure, face-to-face dimension and installation type (wafer, lug or double-flanged), as well as the materials of the body, disc and seal, medium, operating temperature and type of operation. For actuated valves, the flange pattern and shaft connection for the actuator are also needed. The data from the nameplate is the most important basis for this.
Can a butterfly valve be used for control?
To a limited extent, yes. Many butterfly valves are suitable for coarse throttling, but their characteristic is not designed for fine control tasks. At small opening angles, high flow velocities, cavitation and rapid wear of the disc and liner are likely. For precise control, special control butterfly valves or control valves are used.