Butterfly Valve

Butterfly valves have been around for a long time, and are used for a variety of applications. They made their first appearance during the 1930s, and have been utilized by several industries ever since. Often made out of cast iron, butterfly valve's name is based from the functionality of its disc. There are a few different types of butterfly valves, however, they fall into two basic types - Lug and Wafer valves.

Butterfly valves are classified as "quarter-turn" valves. When the metal disk that's part of the valve’s design is rotated a quarter of a turn, it opens or closes. The disk, referred to as the "butterfly" is attached to a rod. When the butterfly valve is opened all the way, the disc rotates (a 1/4 turn), allowing for a nearly unrestricted passing of the fluid. You can also open the valve gradually to reduce flow. Turning the butterfly (disk), to close the valve, blocks the passage of the fluid. This is due to the disc always being perpendicular or parallel to the flow, resulting in a pressure decrease regardless of the position it is in.

WAFER BUTTERFLY VALVE

A wafer butterfly valve's function is to retain a seal to protect against dual-directional pressure differential in the flow of fluid. In other words, the wafer version of butterfly valves was designed to hold a tight seal, safeguarding against bi-directional pressure differential in order to avoid any backflow in systems that have been manufactured for uni-directional flow. This is accomplished by using a tightly fitted seal, such as an O-ring, gasket, precision machined, along with a flat valve face on the downstream and upstream sections of the valve.

Both lug and wafer butterfly valves are used in a number of applications for industrial sectors that include food processing, pharmaceutical, chemical, oil, water as well as waste water management. The valves utilized in these industries are generally manufactured in compliance with the "Pharmaceutical Quality/Manufacturing Standard", cGMP (current good manufacturing practice) guidelines. Butterfly valves for the most part have replaced ball valves in a lot of industries. This is especially the case for those dealing with petroleum because of they are less expensive and easy to install. It's important to note that pipelines that contain butterfly valves can't be 'pigged' for cleaning. "Pigging" is the process of making use of devices referred to as "pigs" to carry out a variety of maintenance operations.

Butterfly valves have been around for a long time, and are used for a variety of applications. They made their first appearance during the 1930s, and have been utilized by several industries ever since. Often made out of cast iron, butterfly valve's name is based from the functionality of its disc. There are a few different types of butterfly valves, however, they fall into two basic types - Lug and Wafer valves.

Butterfly valves are classified as "quarter-turn" valves. When the metal disk that's part of the valve’s design is rotated a quarter of a turn, it opens or closes. The disk, referred to as the "butterfly" is attached to a rod. When the butterfly valve is opened all the way, the disc rotates (a 1/4 turn), allowing for a nearly unrestricted passing of the fluid. You can also open the valve gradually to reduce flow. Turning the butterfly (disk), to close the valve, blocks the passage of the fluid. This is due to the disc always being perpendicular or parallel to the flow, resulting in a pressure decrease regardless of the position it is in.

LUG BUTTERFLY VALVE

The lug version of the butterfly valve's design is similar to a 3-piece ball valve in that one end of the line can be taken off without having an effect on the opposing side. This can be executed by using threaded inserts, flanges, along with two sets of lugs (bolts) that don't utilize nuts since each flange features its own bolts. It's also important to note that you don't need to shut down the entire system in order to clean, inspect, repair, or replace a lug butterfly valve (you would need to with a wafer butter valve).

The double-offset or high-performance butterfly valve has a disc with two offsets and can be rated up to 1480 psi. Similar to a single-offset design, the stem is located behind the disc. With the high-performance butterfly valve, the second offset’s stem is moved once more off the center of the disc to one side. This geometry of offsets enables the 90 degree disc rotation to “rub” over the seat for only one to three degrees of the 90 degree rotation.

The double-offset butterfly valve is used in systems requiring higher pressure resistance. The disc is positioned in the center of the pipe bore and arranged to increase sealing ability and decrease wear to the valve. WKM high-performance butterfly valve is ideal for handling water, oil, steam, and gas in a cost effective, light weight design.

Both resilient and high-performance butterfly valves can be operated by handles, gears, or actuators. These devices move the valve disc to the optimal position for complete shutoff or fully open the valve. Resilient and high-performance butterfly valves are used mainly in the water, chemical and petrochemical industries, but can also be used in fuel handling systems, power, and many other applications.

The last type of butterfly valve is the triple-offset butterfly valve. This type of butterfly valve is applied in difficult services where reliable performance under harsh conditions is needed. Exactly like a double-offset valve, the stem is located behind the disc and offset to one side (double-offset). The third offset is the geometry of the seating surface. This seating surface creates a sort of cone-shape of the disc and seat, which wedges into the seat with very minimal contact between the sealing surfaces until fully closed. By reducing the amount of contact that the seat has with the disc, sealing becomes more efficient and the life of the valve is extended.

Triple offset butterfly valves are commonly used in steam, chemical, refining, and offshore oil and gas applications up to 1400° F (760° C). The rugged metal seats can also withstand a high degree of abrasion and shock and, with appropriate material selection, can also be utilized in cryogenic services such as LNG and NPG facilities.

THE BENEFITS OF TRIPLE-OFFSET VALVES

• ‘Cam-action’ and ‘right angled’ conical sealing design ensures the metal sealing components are never in contact until its final degree of closing. This results in repeatable sealing and a vastly extended valve life.

• Metal-to-Metal sealing ensures bubble tight shut-off, resulting in zero-leakage performance.

• Suitability to harsh media because the construction of the valve features no elastomers or materials typically affected by corrosion.

• Geometric design of sealing components provides friction-free stroking throughout the valve. This extends the valve life and allows a lower torque-actuator to be fitted.

• There are no cavities between sealing components, resulting in no clogging, low maintenance and extended valve life.