Ball Valve vs. Butterfly Valve – A Deeper Look At Pros & Cons
Valves are fluid control devices that are used to manage the flow of media in a piping system. This involves directing, controlling and regulating flow. There are various types of valves that, though they perform the same function of fluid control, are of different builds or best suited for different applications.
This article comparatively explores ball valves and butterfly valves, two of the most commonly used quarter-turn valves. The following explains their construction, mode of operation, applications, benefits, and limitations, before analysing the different scenarios in which each valve will be best suited.
Ball valves
Ball valves are quarter-turn valves that are either manually controlled or automated using electrical or pneumatic actuators. Ball valves operate using a horizontally hollowed-out sphere/ball to control flow. The ball swivels on the vertical axis and is connected to an externally located lever via a stem.
The lever is used to control the valve. It also indicates the position – open or closed – of the valve at any given time. As ball valves are quarter-turn valves, i.e. the ball can only turn 90°. When the hole is perpendicular to the flow direction, the valve is closed, and the ball's solid portion shuts off the flow. On the other hand, when the valve is open, the hole is aligned with the flow path, allowing the fluid to flow through.
Ball valve
However, ball valves do not operate in open and closed positions only. These valves can be set to partially open/partially closed positions using the lever. This feature of ball valves makes them suitable for not only blocking/permitting flow, but also for regulating it.
Types of ball valves
There are numerous types of ball valves that can be classified according to different categories. Some of these are as follows.
By number of ports
While most ball valves are 2-way, i.e., having two ports, there are also 3-way and 4-way ball valves that serve different circuit functions. 3-way ball valves rank immediately after their 2-way counterparts in terms of ubiquity. These ball valves typically have either L-shaped or T-shaped bores, allowing them to achieve circuit functions such as distribution and mixing of flows. 3-way valves are commonly referred to as T valves because of their semblance to the letter “T.”
3-way ball valve with manual lever
By ball design
Ball valves are also classified by ball design – into floating and trunnion valves. In the floating ball design, the ball is held in place by the valve seats. On the other hand, the trunnion ball design sees the ball also supported at the top and the bottom. The trunnion ball design is used for large diameter ball valves with high operating pressures.
By housing assembly
Another category for classifying ball valves is the housing assembly. The housing, which is the main valve body that encloses the ball, may be one-piece, two-piece, or three-piece. One-piece valve housings are a single unit. While these are the least expensive, they cannot be disassembled for repair or cleaning.
On the other hand, two-piece valves can be dismantled. However, they have to be disconnected from the pipe to do this. Lastly, three-piece pipes are made of different pieces that are bolted together. The centre section of these valves can be disassembled or removed without having to uninstall the end connections from the pipe.
By build variation
Apart from the loosely defined standard ball valve construction, some ball valve types may have certain extra features for specific purposes. One such type is the vented ball valve. At first glance, vented ball valves look like regular ball valves. However, these valves' balls feature a small orifice drilled into the solid portion of the valve.
This feature allows pressure or any trapped medium to escape when the valve is closed. It is critical in high-pressure and extreme temperature applications.
Vented ball valve
Ball valves also vary by connection ports. A ball valve may have a threaded, welded, flanged, tri-Clamp, or true union connection.
Applications of ball valves
Ball valves are used in countless applications across various industries. This wide usage results from their availability in a wide range of builds, sizes, and materials and their excellent control abilities. They can be used for start/stop operations, as well as mixing, directing, and regulating flow.
These valves have numerous domestic and industrial uses and can be found in gas plants, water systems, industries, refineries, distilleries, homes, and many others.
Benefits of ball valves
Ball valves are quick-acting, requiring only a 90-degree turn to completely open or close.
They provide tight sealing, completely preventing the flow of media once in the closed position.
They allow for precise and reliable flow regulation
The spherical build of the stopping mechanism allows it to withstand high pressures
When in the fully open position, ball valves rarely cause pressure drops as the ball doesn't interfere with the flow
A ball valve will always turn, regardless of the inflow pressure
Limitations of ball valves
Ball valves are relatively expensive
They are larger and heavier than their counterparts of the same capacity, making it impossible to use them in certain scenarios.
Butterfly valves
Like ball valves, butterfly valves are quarter-turn valves that control the flow of the medium. These valves may be manually controlled or automated using actuators. The closing mechanism in a butterfly valve is an upright, flat, circular disc that turns on the vertical axis.
The disc is usually attached concentrically or eccentrically to the top and bottom of the valve, with the stem running along the disc's side. The stem extends out of the valve, where it is connected to the controlling lever.
Butterfly valve
Butterfly valves turn by 90°, moving from the fully open to the fully closed positions and vice versa. The disc's turning motion resembles the motion of a butterfly's wing, hence the name “butterfly valve.”
When the valve is fully open, the disc is perpendicular to the flow direction, with the thin edge of the disc facing the flow. On the other hand, when it is fully closed, the disc's flat face aligns with the flow, completely blocking it.
Butterfly valves can be placed in partially open/partially closed positions, but this is used more for reducing flow rate than precise regulation.
Types of butterfly valves
There are various types of butterfly valves that each combine a set of features. As a result, butterfly valves can be classified according to different categories, using these features.
By disc design
Based on disc design, butterfly valves can be classified as concentric and eccentric. Concentric butterfly valves are more common, with the stem passing through the disc's centreline. These valves are also known as zero offset valves. On the other hand, in eccentric butterfly valves, the stem doesn't pass through the disc's centerline.
Eccentric butterfly valves may be single offset, in which the stem is located directly behind the centreline; double offset, in which the stem is placed behind the disc, but with an extra offset along the lateral axis of the disc; and triple offset, in which there is an additional offset between the disc and the seat contact axis.
By build
Butterfly valves are of different builds, with the major difference between them being the mounting features. The most common butterfly valve builds are lug butterfly valves and wafer butterfly valves. The lug variants feature threaded lugs around the valve flanges. These lugs are used to connect the valve with bolts. Wafer valves, on the other hand, do not have attachment lugs. Instead, they are sandwiched between pipe flanges.
Applications of butterfly valves
Butterfly valves are sought after due to their versatility and functionality. They come in a wide range of sizes. Butterfly valves can be found in industrial plants, wastewater processing plants, water supply systems, and many others.
Benefits of butterfly valves
Butterfly valves are quick-acting, requiring only a 90-degree turn to completely open and completely close.
They provide good open/close control.
They are cheaper than ball valves of the same capacity
Because of their design, butterfly valves are smaller and lighter than their ball counterparts. This makes it easy for them to fit into tight spaces and complex circuits
Limitations of butterfly valves
They do not provide 100% sealing and are relatively leak-prone
By design, the disc is always in the flow path. While the interference may be minimal, it still has the potential to result in a pressure drop
Butterfly valves are not suitable for high-pressure applications as the disc is unable to reliably withstand such pressures.
There are inflow pressure limits above which the valve may fail to turn.
Ball valves vs. butterfly valves
Both ball and butterfly valves are used in a wide range of applications. These quarter-turn valves are used to control the flow of fluid in piping systems. They are available in numerous materials, including brass, PVC, stainless steel, steel, copper, etc.
Butterfly valves provide good start/stop control. For applications in which only this is required, butterfly valves are sufficient. When cost is a major consideration, butterfly valves are the better option. However, their relatively fragile build makes them unsuitable for high-pressure applications. They are also not suitable in applications requiring precise control as they may leak. For such applications, the sturdy build of ball valves makes them a better choice.
On the other hand, ball valves are relatively large and cumbersome compared to butterfly valves of the same capacity. This makes butterfly valves great for tight spaces.
