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What are the different types of Butterfly Valves?

Valves are devices that are installed in piping systems to control the flow of a liquid. One of the more ubiquitous types, the Butterfly Valve, consists of a disc mounted on a shaft that rotates a quarter of a turn to permit or stop the flow of liquid. It owes its popularity to being lightweight, durable and easy to install. Its relatively simple design makes it easy to manufacture and, hence, cheaper than most other valves.

Additionally, it offers the following advantages:

  • It is compact and lighter than most valves for the same application.
  • It is available in sizes ranging from 2 inches to 20inches and can be much bigger if needed.
  • It requires less maintenance as it has fewer moving parts.
  • It is well suited for applications with differential fluid pressure.
  • It can be used to completely isolate the fluid flow.
  • It can also be used to regulate fluid flow, unlike gate valves.

There are different types of butterfly valves based on how they are connected to the piping and how they are designed.

Classification based on connection:

Wafer type butterfly valve: A wafer style valve is sandwiched between the two pipe flanges and is connected with one set of bolts. Since the entire piping and valve system are connected, you cannot remove one side of the piping while keeping the valve and another side intact. You will have to disrupt the whole setup. A wafer style connection is appropriate in case of a uni-directional flow, where it can prevent backflow.

  • Lugged butterfly valve:

The valve is installed between the two pipe flanges with separate sets of bolts on either side, with a lug inserted in between. Thus, any side of the piping can be dismantled without disturbing the other side. The lug valve can be a connecting valve or a dead-end service. The pressure is adjusted accordingly for either use. The valves used for dead-end service generally have a lower pressure rating. Unlike the wafer-style, lugged valves carry the weight of the piping through the valve body.

  • Double flanged:

Especially suited for large pipes, the double flanged valve is flanged on both sides. It is connected to the piping flanges through two separate sets of bolts like the lugged and thus can be used for dead-end services.

Butterfly valves can also be categorized based on design:

Depending on how the disc is positioned against the seat of the valve, there are concentric and eccentric valves.

  • Concentric valve:

It is a standard valve where the shaft of the disc runs through its centre. In the closed position, the disk sits flat against the seat. Generally, the outer diameter of the disc is bigger than its inner diameter, thus achieving a bubble-tight shut off in the closed position. The disc and seat are constantly in contact, causing friction to build up at times. It can be used in non-critical applications with pressures up to 150psi.

  • Eccentric valve:

In the concentric valve, there is undue friction between the disc and the seat. The eccentric valves were designed to eliminate that and can thus be used in higher pressure and temperature applications. The commonly available eccentric valves are double offset and triple offset.

  • Double-offset:

In these valves, the shaft does not run through the centre of the disc. Instead, it is offset both from the centreline of the disc as well as that of the pipe. The friction in this type of valve is reduced and occurs only at acute closing and opening angles.

Its design makes it suitable for high-pressure applications – up to 600psi. It can also be used for throttling the flow, unlike the concentric type.

  • Triple-offset:

Along with the two offsets of the double-offset valve, a third offset is achieved by changing the seat’s profile, making it oblique. It minimizes friction to a negligible level. The design also allows for both the disc and seat to be made of metal, so the valve is excellent for high-temperature and pressure environments. The reduced friction ensures a higher lifetime of triple-offset valves. They are highly suited for emergency valves on storage tank inlets, outlets and overflow lines.

The popular Butterfly Valve has proven its mettle since the times of the first steam engine. Advancements in material science and manufacturing technology, along with design efficiency, have only increased its applicability. There’s little doubt that this versatile valve is here to stay!

Red Note: 30 September 2022

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