A wafer-style butterfly valve is a versatile, compact valve type often used in piping systems to regulate flow. It typically features two or four non-threaded holes that allow it to be installed between two flanges, where it is held in place using a lengthy bolt or threaded rod. This design pulls the flanges together to secure the valve, ensuring it stays firmly in position. The primary purpose of the wafer butterfly valve is to maintain a tight seal, preventing double-directional pressure differentials in liquid flow.
Purpose and Functionality of Wafer Butterfly Valves
The wafer-style butterfly valve was specifically developed to prevent backflow in systems designed for unidirectional flow. It achieves this by employing a precisely fitted seal, such as a gasket or O-ring, that is precision-machined for a reliable fit. This seal acts as a barrier, ensuring the valve does not leak under pressure, even with bi-directional flow conditions.
These valves are most commonly used in applications requiring tight, reliable sealing. Typically, the valve features four holes that align with the pipeline it is connected to. The valve is designed to fit snugly between two pipe flanges, and its strong sealing properties are reinforced with rubber or EPDM valve seats, offering a durable and leak-proof connection. The wafer-style butterfly valve is compatible with most flange standards, making it highly versatile in various industries.
Limitations of Wafer Butterfly Valves
Unlike lug-style butterfly valves, wafer butterfly valves are not suitable for use as pipe ends or for end-of-line services. If maintenance is required on either side of the valve, the entire pipeline needs to be shut down, as both flanges are typically needed to keep the valve securely in place. This key distinction makes it essential to carefully evaluate whether a wafer or lug butterfly valve is more appropriate for a particular application.
In contrast, wafer butterfly valves are often designed for either electric or pneumatic actuation. The material choice for the disc and seat is crucial and should be selected based on the specific application and flow media to ensure durability and performance.
Key Components of a Wafer Butterfly Valve
Valve Body: The valve body of a wafer-style butterfly valve is designed to fit between two pipe flanges, with no lugs protruding from the body. The valve is "sandwiched" between these flanges and is secured with bolts, which also prevent the weight of the pipe system from being directly passed through the valve body. Compared to lug-style valves, wafer butterfly valves are more cost-effective and lightweight.
Stem: The valve stem can either be a one-piece or two-piece design. In resilient seated designs, the stem is protected from the flow media, allowing it to be made from more cost-effective materials. There are two types of stems: wetted and non-wetted. Wetted stems are exposed to corrosive or erosive media and require materials compatible with the flow media. Non-wetted stems, on the other hand, are shielded from such media to enhance durability.
Disk: The disc inside the wafer butterfly valve controls the flow of media through the valve. Two main types of discs are used: concentric and eccentric. The concentric disc is simpler, with the stem passing through the centerline of the disc. This type is typically used for low-pressure applications. Eccentric discs are designed to move the stem away from the centerline, preventing the disc from coming into contact with the seal, thus extending the valve's lifespan.
Seat: The seat of the valve is made from elastomers or polymers and is attached to the inner diameter of the valve body. When the disc presses against the seat, it creates a seal that stops the flow of media. The addition of elastomers or polymers ensures a leak-proof and tight seal, which was not possible with the original metal-on-metal designs.
Hand Lever and Gear: Smaller wafer butterfly valves often use a steel hand lever, which is treated for durability and precision. The lever typically includes a locking mechanism for secure valve positioning. For larger valves, a gear system is employed to boost torque and control the opening and closing speed. These gear-based valves are self-locking and irreversible, making them highly reliable in various applications.
How Wafer Butterfly Valves Work
Wafer butterfly valves operate similarly to other quarter-turn valves. The metal disc, commonly known as the "butterfly," is positioned on a rod inside the valve. When the valve is closed, the disc prevents the flow of liquid. When the valve is opened, the disc turns 90 degrees (a quarter turn), allowing media to flow freely through the valve. The degree to which the valve is opened determines the flow rate. A fully open valve allows for maximum flow, while a partially open valve restricts the flow, making wafer butterfly valves ideal for regulating flow.
Pros and Cons of Wafer Butterfly Valves
Advantages:
- Low Pressure Drop: The streamlined disc design minimizes pressure drop and flow restriction.
- Quick Actuation: The valve only requires a 90-degree turn to move from fully open to fully closed, making it a quick-acting valve.
- Flow Regulation: The valve design is well-suited for regulating flow with minimal turbulence, especially when partially opened.
- Cost-Effective: Wafer butterfly valves are generally more affordable and lightweight, making them ideal for large applications.
Disadvantages:
- Pressure Drop: While low, there is still a modest pressure drop when the valve is fully open.
- Maintenance Challenges: These valves often need to be overhauled in a workshop rather than being maintained on-site.
- Limited Cleaning Tools: Pigs, used for cleaning and inspecting the interior of pipes, cannot be inserted into butterfly valves.
Common Applications of Wafer Butterfly Valves
Wafer butterfly valves are widely used across various industries, including:
- Aerospace
- Compressed Air Systems
- Petroleum and Gas Processing
- HVAC Systems
- Water Treatment
- Irrigation Systems
- Fire Protection Systems
Due to their versatility, these valves are particularly effective in handling large volumes of water, slurry, and air, making them an excellent choice for many industrial processes, including cooling systems in power plants, mining operations, and shipyards.
Conclusion
The wafer butterfly valve stands out due to its simplicity, compact size, and reliability in various industrial applications. Its robust design ensures a tight seal, making it a top choice for controlling fluid flow, especially in systems requiring bi-directional pressure control. However, it is important to weigh its limitations against the benefits and ensure it is suitable for your specific needs before installation.
