How Butterfly Valves Work, their Types, Advantages, and Symbols

The smaller butterfly valves are usually operated manually, while the larger ones are usually motorized. Due to their high flow capacities, butterfly valves enable smaller units to be used, which reduces weight, cost, and space requirements. Due to their two wetted parts and wide range of valve linings, butterfly valves isolate the body from the flowing media, thus eliminating the need for expensive exotic materials.

With a smooth contoured, crevice-free disc, butterfly valves produce lower torques and are easier to install, maintain, and service.

Butterfly Valve Uses

There is a wide range of applications for Butterfly valves. In addition to water supply, wastewater treatment, slurry services, fire protection, air and gas supply, vacuum services, lubrication systems, chemical and oil industries, fuel handling systems, power generation, compressed air, gas, steam, food processing, pharmaceutical, marine, and sanitary valve applications, butterfly valves are commonly used. Butterfly valves can be used in a variety of applications.

• Applications involving constant loads
• Applications with limited space
• Valves used for throttle control

Components of a Butterfly Valve

Valve body: The Butterfly valve body fits two pipe flanges, the most common body design is lug-and-wafer.

Butterfly valve disk: The disk (disc) is the element that prevents flow. Various disk designs and orientations are used to improve flow, sealing, and operating torque.

Valve Stem: There are two types of stems for butterfly valves: one-piece and two-piece. There should be no galling potential between similar corrosion-resistant materials in the stem design.

Butterfly valve Seat: In butterfly valves, the disk edge and the seat are fitted in an interference fit to provide shutoff. Bonding, pressing, or locking the seat into the body are all possible options.

Depending on the manufacturer, butterfly valve seats have different designs. PTFE seats are popular because they are made from a single piece of flexible material. Because there are no metallic springs or O-rings to limit the temperature or corrosive conditions that the PTFE seat can be exposed to, the single-piece seat is significant. Line pressure causes the seat to follow the natural deflections of the disc under pressure by pressurizing the entire cross-section.

Advantages of Metal Seats in Butterfly Valves

• A good level of tightness
• There are no jams
• Controlled smoothly
• The torque is low
• A wide range of temperatures
• A low level of cavity relief
• Good resistance to corrosion

Functions of a Butterfly Valve

• Flow regulation: By simply turning the valve wheel, you can control or regulate the flow. With a flow controller, you can automate the process.

• Prevention of Backflow: Backflow prevention can be achieved in some situations with butterfly valves.

Types of Butterfly Valves

Butterfly valves can be classified into different types based on their disc closure design, their connection design, and their actuation method.

• The design is based on disc closures
• Butterfly valve with a concentration
• Butterfly valve with eccentricity
• The single-offset system
• Offsets with two
• Offsets in threes

• Based on the connection of pipes
• The lug type
• The wafer type
• A butterfly valve with a flange
• Butterfly valves with butt welding for high-pressure applications

• According to the method of operation
• The manual method of actuation
• Operated by a lever
• Operated by gears

• Actuation by automatic means
• Powered by electricity
• A pneumatic system
• A hydraulic system

• Based on Seat Material
• Soft Seated
• Metal Seated

Concentric Butterfly Valve

A concentric butterfly valve is the simplest type of butterfly valve. Discs are designed with the valve stem passing through the centerline. Zero-offset valves are also known as zero-offset valves. Low-pressure services are handled by butterfly valves with concentricity.

Eccentric Butterfly Valve

Eccentric butterfly valves do not have stems that pass through the disc's centerline. Offset valves can be divided into three types.

• Single-offset valves have the stem located directly behind the centreline of the disc.
• Double-offset butterfly valves have a stem behind the disc with an additional offset on one side.
• It is necessary to use a triple offset butterfly valve for highly critical applications. A third offset lies between the disc and seat contact axis.
  
  

Lug Type Butterfly valve

A lug-style butterfly valve has threaded lugs on the outside of the valve body. The valve is attached to the piping flanges using two sets of studs. Each flange has its bolts, so it is possible to disconnect one end without affecting the other.

Wafer Type Butterfly Valve

The Wafer type butterfly valve is sandwiched between two pipe flanges, and flange bolts surround the valve body. The most economical butterfly valve is this one. Both flanges and valve bodies are covered with long bolts. Wafer butterfly valves seal against bi-directional pressure differences in fluid flow. It is designed to prevent a tight seal and a two-way pressure difference when used with the wafer version of the butterfly valve.

Wafer vs Lug Style Butterfly Valve

There are several differences between a wafer-type butterfly valve and a lug-type butterfly valve. Please refer to the following paragraphs for more information.

Lug-style butterfly valves are mounted to piping flanges with bolted connections using threaded lugs. A wafer-style butterfly valve, on the other hand, does not have attachment lugs. The piping is usually aligned with four holes in the connectors. An in-line valve is clamped between two flanges on the pipe.

Wafer-style butterfly valves cannot be used for end-of-line service, but lug-style butterfly valves can. Whenever there is a maintenance requirement on a line with water style butterfly valves, the entire line must be shut down.

Butterfly Valve Sizing

It is not the nominal diameter of the pipe that determines the size of butterfly valves used for control purposes. To achieve correct control characteristics, the size must be determined based on operating characteristics. The opening angle characteristics should be considered when determining the size. Some butterfly valves are typically designed with approximately equal percentage characteristics over an opening of 600.