What Are the Advantages of Butterfly Valve Control？

Butterfly valves are a family of quarter-turn rotational motion valves that are used in pipelines to shut-off flow. It is often said that butterfly valves can be used to regulate the flow. However, we do not recommend doing this, as it can damage the valve disk and have a negative effect on the sealing properties. They are used in a wide variety of process media and industries especially in water supply, collection, and distribution, as well as pumping stations, and have a broad range of use cases especially in flow isolation. A couple of their key advantages over other valve families are their simple construction and compactness, resulting in the end products being of lighter weights and lower cost and with smaller installation footprints and faster actuation speeds.

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Hawle butterfly valves are flanged double eccentric type (double offset) type. The double offset or eccentricity refers to the fact that this valve design involves two offsets of the disc from the valve body’s centre or the axis of rotation of the stem.

Below are the major butterfly valve components:

• Valve Body
  The valve body fits between the pipe flanges - the most common end connection types being flanged, double lug, and wafer types.
   
• Disc
  Attached to the valve body is the disc that functions as a gate that stops or throttles fluid flow; it can be considered equivalent to a gate in a gate valve, or a ball in a ball valve. The disc is typically bored to receive the stem, or shaft. There are many variations in disc design, orientation, and material in order to improve flow, sealing, and/or operating torque. For example, Hawle’s k double eccentric disc is designed to reduce seal wear and “scuffing” as well as operating torque requirements.
   
• Seat
  Lining the internal valve body is a strong elastomer or metal anti-leak seal that secures the disc in place in the closed position in order to achieve complete shutoff. The k series’ stainless steel weld filled and microfinished integral body seat ensures a corrosion and erosion resistant seat face. With this special type of seat design, it is possible to manufacture the valve drop tight according to EN –A requirements.
   
• Stem
  The valve shaft, often also referred to as the stem, is the component that connects the disc to the actuation mechanism and transmits the torque through itself.
   
• Seals
  Seals are present at multiple interfaces within the valve to either ensure a tight seal during operation or to isolate the process media from the valve’s internal components for a more flexible and cost-efficient design.

Sealing on seat face is ensured by a continuous T-profile resilient sealing ring which is held on the periphery of the disc by a retaining ring, preventing the sealing ring from rolling out. In the closed position, the sealing ring is pressed against the seat face, providing a tight seal on both the upstream and downstream ends. In the open position, the sealing ring is completely unstressed due to the double eccentric disc design.

By eliminating interaction between the process media and the stem/shaft, the multiple O-ring shaft sealing system ensures a maintenance-free sealing for the entire life span of the valve. Besides, there are smaller more common components such as the bushings, bearings, and fasteners that are part of most other valve constructions as well. Details on some of the components on the actuation end, such as the handle, lever, gearbox, and handwheel will be covered in the actuation section.

The construction of a butterfly valve is relatively simple, with the rotation of the valve disc controlling the fluid flow. In the closed position, the disc blocks the valve bore while in the open position, the disc is oriented perpendicular to the flow direction to allow flow. Butterfly valves generally provide bi-directional flow and shutoff capability. However, they are not full-bore, which renders them unsuitable for pigging or swabbing. The body material is ductile iron with an epoxy powder coat on both internal and external surfaces. The valves are typically operated by handwheels, gears, or actuators, or a combination thereof, according to the specific application requirement and technical specifications. We will be discussing the actuation methods later in the article.

There are multiple ways to operate, or actuate, a butterfly valve - manual, semi-manual, or fully automatic.

• Electric: Uses an electric actuator for controlling the valve with a 4-20mA control signal and are typically used for high precision regulation and time-sensitive application.
   
• Pneumatic: Also used for high precision application and uses compressed air for actuation.
   
• Hydraulic: Typically used for applications requiring large torques for opening and closing the valve, such as high pressure and high viscosity applications.
   
• Manual: Manually operated butter valves make use of a handwheel, crank, or lever to operate the valve. Smaller manual valves are typically fitted with a lever. For larger sizes, handwheels are provided and are accompanied by a gearbox to transfer the torque with a high mechanical advantage. Another way of manual actuation is in use cases where the valve is buried underground without a manhole; in such applications, actuation is done with an extension spindle, adapter / square cap, and a corresponding T-key from the ground level.

Due to inherently lower torque requirements, sizing and installing actuators are less expensive for butterfly valves compared to others, like gate valves.

The k series comes standard with a handwheel actuation and wormwheel gearbox with a self-locking design feature that minimizes gear backlash and guarantees the correct operation and tightness of the end device. It is also compatible with external actuators with an ISO top flange for mounting of multi-turn actuators.

On the application side, butterfly valves are especially well-suited for the handling of large fluid flows of fluid, such as in water distribution systems (pumping stations or water collection and transmission) and water treatment plants (seawater or raw water). This, along with their availability in a large range of sizes including up to DN (55 inches), makes them ideal for drinking water distribution applications. They are typically used for flow isolation devices and are normally fully open or fully closed. Hawle provides butterfly valves geared towards specific application areas and are available on demand. The Özkan double eccentric double flanged butterfly valves, for example, are offered for high pressure applications upto 40 bar (PN 40) and up to DN .

The Hawle k series double eccentric butterfly valves come in sizes ranging from DN 150 up to DN with pressure ratings of both PN 10 and PN 16. Additionally, design feature optimizations such as the double offset, or double eccentric (e1 and e2 as seen above) disc further reinforces its advantages of achieving a tight seat seal through full circle sealing, and improves the service life of internal components while lowering operating torque requirements.

A butterfly valve is a device that allows you to achieve better flow control. The design uses a metallic disc that rotates a quarter-turn at a time around a fixed-stem axis. The 90-degree turns provide quick-action control between open and closed positions. In addition, the disc is generally sized equally to the internal diameter of the adjoining pipe to give full-color capability.

Naturally, butterfly valves are manufactured in various sizes and design configurations to provide specific flow control functionality. As a result, varying applications and industries, including everything from HVAC and fire protection to slurries and sanitation.

So, when does it make sense to use a butterfly valve in your pump or vent system? Let’s take a look at butterfly valves’ advantages and disadvantages to help you make a more informed decision.

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ADVANTAGES OF BUTTERFLY VALVES

Lightweight and Compact

Butterfly valves are great for several applications because they are very lightweight and provide reasonable flow control in a compact design. You will generally want to use a metal-seated valve for more extreme fluid processing, while a soft-seated butterfly valve is best for applications with low pressures and temperatures. The butterfly disc takes up little space but offers enough strength for most pump systems.

Simple and Cost Effective

Butterfly valves are very simple in design and have minimal maintenance requirements. They are easy to install and operate. Plus, they are typically much less expensive than a ball valve of the same size. They do not require much torque to operate effectively and can be automated for energy-efficient operation.

Quick and Efficient

The 90-degree turning radius allows for quick sealing upon actuation, which provides more accurate flow control with minimal effort to turn the valve on and off. Different butterfly valves are to consider, including zero-offset, double-offset, and triple-offset. The pressure will usually determine which type you need. The higher the offset, the more pressure the valve can handle.

Pressure Control

In addition to precision flow control, butterfly valves are excellent for pressure control. They experience minimal pressure drop during operation before the fluids recover energy quickly after leaving the valve. This keeps the pump system running efficiently with consistent fluid pressures.

DISADVANTAGES OF BUTTERFLY VALVES

Corrosion and Viscous Fluids

Viscous and corrosive fluids tend to scour against the discs of butterfly valves during operation, which can lead to rapid deterioration of the disc and loss of sealing pressure. If you are processing highly viscous liquids, you may want to consider a more robust ball valve or gate valve instead of a butterfly valve.

Cavitation and Choked Flow

When the valve is in an open position, it does not provide a complete port because of the disc. This can lead to excess debris accumulation around the valve in specific applications, cavitation concerns, or the possibility of choked flow. A ball valve may be a better solution if a full port is required.

No High-Pressure Throttling

A butterfly valve has an opening restricted between 30-80 degrees, making them efficient for low-pressure throttling applications. However, higher pressures may achieve better results with a globe valve. To learn more about butterfly valves from the leading valve manufacturers and determine if this is the correct solution for your application and pump system, contact DXP Pacific today. Let our pump experts help you find the right equipment to optimize your production.

If you want to learn more, please visit our website Butterfly Valve Control.