Butterfly Valve Overview

A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disc. Butterfly valves are generally favored because they are lower in cost compared to other valve designs as well as being lighter in weight, meaning less structural support is required. The disc is positioned in the center of the pipe, passing through the disc is a stem connected to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow.

There are three different types of butterfly valves defined by the orientation of the stem to the disc and the seating angle that the disc closes on.

 

Resilient Seated Butterfly Valves (Zero Offset)

center-line-butterfly-valveConcentric valves have zero offset and are often called resilient seated butterfly valves. The disc rotates around the center axis allowing for a potential 360° rotation. Selaing is achieved by the disc deforming the soft seal resulting in full friction through the full operating cycle.  This valve typically has a rubber (or resilient) seat and relies on the disc having a high level of contact with the seat to effect a seal.

For more information and vendor specific information, visit our Resilient Seated Butterfly Valve page.

 

High Performance Butterfly Valve (Double Offset)

HPBV-Lug-StyleOften called Doubly eccentric butterfly valve,  high performance butterfly valve or double offset butterfly valve. As the name implies, the double offset butterfly valve consist of two stem offsets from center. To allow displacement of the seat the shaft is offset from the center line of the disc seat and the body seal (offset one) and the center of the bore (offset two). This creates a cam action during operation to lift the seat our of the seal resulting in friction during the first 10 degrees of opening and the final 10 degrees of closing. Double offset valves can be supplied with soft or metal seats with a variety of material choices depending on application. Design limitations on temperature and pressure restrict double offset valves to ANSI 600 and less than 1000°F.

For more information and vendor specific information, visit our High Performance Butterfly Valve page.

 

 

Triple Offset Butterfly Valves

As the name implies, there are three separate offsets designed into this valve. Similar to the double offset butterfly valve, two of the offsets apply to the location of the shaft with respect to the center line of the bore and the center line of the disc/seat sealing surfaces.

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.

The TOV features unique designs in the disc /shaft engagement and in the precision-machined seat and seal ring of identical eccentric shape. These features, combined with the eccentric movement, provide longer cycle life, lower operating torque, and increased temperature capability.  Additionally, the torque-seated resilient metal seal ring assures consistent bi-directional zero leakage performance. TOVs are typically metal–seated, unlike single and double-offset butterfly valves, which allows it to achieve “zero leakage” in either direction for extreme services. The true triple-offset geometry of the TOV allows for “bubble-tight” sealing to create a fully bi-directional “zero-leakage” shut-off valve.

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. “Zero leakage” and “Bubble-tight” are per API 598 standards.

For more information and vendor specific information, visit our TOV page.

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