What is a Butterfly Valve?

Butterfly valves are crucial components in water supply systems, offering efficiency and reliability. Understanding their types, actuation methods, and advantages in specific applications is key to their effective use.

 

 

1. What is a Butterfly Valve?
2. Butterfly valve parts
3. Butterfly valve: working principle
4. Butterfly valve actuation
5. Advantages of butterfly valves
6. Double-eccentric Disai butterfly valves

 

Butterfly valves are a type of quarter-turn rotational motion valves commonly used in pipelines to control the flow of fluids. While they are often capable of regulating flow, it is not recommended to use them for this purpose, as it can cause damage to the valve disk and compromise its sealing properties. These valves find extensive use in various industries, particularly in water supply, collection, and distribution, as well as in pumping stations, due to their ability to isolate flow effectively.

One of the primary advantages of butterfly valves is their simple construction and compact design. This results in lighter weight, lower cost, smaller installation footprints, and faster actuation speeds compared to other types of valves.

Disai 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.

 

Butterfly valve parts

Valve Body:
The valve body is the main outer casing of the butterfly valve. It houses the internal components and provides a connection point for the valve within a piping system. the most common end connection types being flanged, double lug, and wafer types.

Disc:
The disc, also known as the butterfly, is a circular or semi-circular plate that rotates inside the valve body to control the flow of fluid. When the disc is perpendicular to the flow, it blocks the flow; when parallel, it allows flow.

Seat:

The seat is a ring-shaped component inside the valve body where the disc comes into contact to form a seal. It ensures tight shut-off when the valve is closed and prevents leakage.

Stem:

The stem is a rod that connects the disc to the external actuator (such as a lever, handle, or actuator motor). It transmits the movement from the actuator to the disc to control the flow.

Seals:

Seals are used to ensure tightness and prevent leakage around the stem and between the disc and seat. They are typically made of rubber or elastomer materials to provide a tight seal under pressure.

The sealing of the valve seat surface is ensured by a continuous T-shaped elastic sealing ring, which is fixed to the periphery of the valve disc by a back-up ring to prevent the sealing ring from rolling. In the closed position, the sealing ring is pressed against the valve seat surface, providing a tight seal at the upstream and downstream ends. In the open position, the sealing ring is completely stress-free due to the double eccentric design.

By eliminating interaction between process media and valve stem/shaft, the multi-O-ring shaft sealing system ensures maintenance-free sealing throughout the valve's service life. In addition, there are smaller, more common components such as bushings, bearings, and fasteners that are also part of most other valve structures. Details of some of the components on the drive side, such as handles, levers, gearboxes, and handwheels, are covered in the drive section.

Butterfly valve: working principle

The design of a butterfly valve is characterized by its simplicity, where the pivotal movement of the valve disc regulates the flow of fluid. When closed, the disc obstructs the valve bore, and when open, it aligns perpendicular to the flow direction to enable fluid passage. Butterfly valves are generally capable of bi-directional flow and provide shutoff functionality. However, their non-full-bore design makes them unsuitable for pigging or swabbing operations. These valves are typically constructed from ductile iron and feature an epoxy powder coat on both internal and external surfaces. They can be operated manually using handwheels, gears, or actuators, or a combination thereof, depending on the specific application requirements and technical specifications. We will delve into the various actuation methods later in this article.

Butterfly valve actuation

Butterfly valves can be operated using various methods, including manual, semi-manual, or fully automatic actuation systems.

1. Electric Actuation: This method utilizes an electric actuator controlled by a 4-20mA control signal. Electric actuators are ideal for applications requiring high precision regulation and time-sensitive operations.

2. Pneumatic Actuation: Pneumatic actuators use compressed air to operate the valve. They are also suitable for high precision applications and offer efficient actuation.

3. Hydraulic Actuation: Hydraulic actuators are used in applications requiring large torques to open and close the valve, such as in high-pressure or high-viscosity applications.

4. Manual Actuation: Manual butterfly valves are operated using a handwheel, crank, or lever. Smaller valves typically have a lever, while larger valves are equipped with handwheels and gearboxes for torque transfer. In cases where the valve is buried underground without access to a manhole, manual actuation is achieved using an extension spindle, adapter/square cap, and a T-key from ground level.

Butterfly valves have lower torque requirements compared to gate valves, making the sizing and installation of actuators less expensive.

The 9881k series of butterfly valves comes standard with a handwheel actuation and wormwheel gearbox featuring a self-locking design to minimize gear backlash. This design ensures correct operation and tightness of the valve. The valve is also compatible with external actuators featuring an ISO 5210 top flange for mounting multi-turn actuators.

Advantages of butterfly valves：
Depending on the application, butterfly valves can offer significant advantages over other types of valves, especially for dimensions over DN 200 (200 mm) in size:

1. Cost-Effective: Butterfly valves are often more cost-effective than other types of valves, such as gate valves or ball valves, especially in larger sizes. The simpler design and fewer parts result in lower manufacturing costs.

2. Compact and Lightweight: Butterfly valves are generally more compact and lightweight compared to other valve types. This makes them easier to install and requires less structural support.

3. Quick Operation: Butterfly valves can be quickly opened or closed with a quarter-turn of the handle, lever, or actuator. This rapid operation is particularly advantageous in applications where fast response times are critical.

4. Minimal Pressure Drop: Butterfly valves have a streamlined design that minimizes pressure drop across the valve. This is beneficial in applications where maintaining consistent flow rates is important.

5. Versatile Application: Butterfly valves can be used in a wide range of applications, including HVAC systems, water treatment plants, and industrial processes. They are suitable for both on/off and throttling applications.

6. Bubble-Tight Shut-Off: When properly installed and operated, butterfly valves can provide bubble-tight shut-off, ensuring no leakage of the fluid or gas being controlled.

7. Low Maintenance: Due to their simple design and fewer moving parts, butterfly valves generally require less maintenance than other types of valves. This can result in lower maintenance costs over the life of the valve.

8. Corrosion Resistance: Butterfly valves are available in a variety of materials, including stainless steel, carbon steel, and PVC, which offer excellent corrosion resistance in different environments.

9. Ease of Automation: Butterfly valves can be easily automated using electric, pneumatic, or hydraulic actuators. This allows for remote operation and integration into control systems for enhanced process control.

Double-eccentric Disai butterfly valves

In terms of applications, butterfly valves are particularly suitable for handling large flows of fluids, such as water distribution systems (pumping stations or water collection and transmission) and water treatment plants (seawater or raw water). This, coupled with their wide range of sizes, including sizes up to DN 1400 (55 inches), makes them ideal for potable water distribution applications. They are typically used in flow isolating devices, usually either fully open or fully closed.

Double-eccentric Disai butterfly valves are available in sizes from DN 200 to DN 4000 and in pressure classes PN 10, PN 16 and PN 40.