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What Are the Characteristics of High Performance Butterfly  Valves and Triple Offset Butterfly Valves?*

Continuing to expound on the previous post on Resillient Seated Butterfly Valves ,this post will focus on the characteristics of  Double Offset , also called High Performance Butterfly Valves, and Triple Offset Butterfly Valves.

What is a High Performance or Double Offset Butterfly Valve?

High Performance Butterfly Valves use a disc offset from the seat center, hence the name Double Offset.

In this configuration, the disc is eccentric, or offset, from the valve seat. As the disc starts to rotate, it moves away from the seat instead of across it. This design actually uses the line pressure to help give it its seal. This feature allows the use of offset butterfly valves in high‐pressure applications such as ethanol or HVAC. It generally uses PTFE or plastic as its seat material, but metal seats are also available to meet fire‐testing specifications like API 607.

Offset Disc Butterfly Valves are comprised of the following components:

• Body
• Retainer Plate
• Seat
• Disc
• Stem
• Stem Seals

Standard double offset butterfly valves come with a polymer seat, usually PTFE, with a metal backup for fire safety. Metal‐to‐metal seats are also available and may provide a higher sealing quality, and allow slightly higher temperatures.

What is a Triple Offset Valve (TOV) ?

A triple offset valve is a torque‐seated valve. In addition to the standard components, the TOV has three offsets. Seats are made of a laminate of metal and graphite and are commonly field replaceable. This valve does not act like a normal butterfly valve that is seated by positioning the disc using a lever, gear or body stop. TOVs are similar to globe valves in that the disc acts like a cone being torqued into a circle seat. The only way to get a bubble‐tight zero leakage seal with a metal seat is to put a cone into a circle. Triple offset valves can be lug, wafer, flanged and butt‐weld. Class rated valves are available from various manufacturers and are manufactured in sizes up to 160 inches. TOVs are adaptable to a wide range of temperatures, from ‐420 to 1200 degrees F.

Because a triple offset valve has three offsets in the stem/disc alignment, its disc rotates 90 degrees with the last +/‐ 1 degree being a straightforward movement. The body seat of the valve is not a perfect cone; rather, it is “offset” and machined at an angle so the disc will match up with no rub when seating. A Stellite overlay ensures a hard seating surface. By tightening the handwheel the valve seats tighter into the seat, typically something only possible with gears. Unlike a gate, ball or high‐pressure butterfly valve, there is no drag across the seat when the disc contacts the seat.

As viewed from the top, the first offset is accomplished by positioning the stem off center to or behind the disc seating face. The second offset moves the stem off centerline of the pipe or valve opening. The third and final offset is the seat cone angle, which is machined into the valve body. When the valve disc is rotated there is no rubbing across the seat. These three offsets enable the TOV to accomplish zero leakage in a metal‐seated valve.

• Main applications for TOVs
•  Steam-distributed (600# & below)
• Universities
•  Hospitals
•  Large buildings
• Government facilities
• Steam production plants
• De-icing/heating for plants
•  Petrochemicals
• Coking
•  Reformers
• Tank switching
• Ethylene
• Butadiene
• Isocyanates – plastics
• Tank and terminal
• Long pattern or gate valve replacement
• Storage of hydrocarbons and chemicals
• Upstream production
• Process equipment
• Separation
• Switching
• Floating production platforms
• Manifolds
• Slurry-tar sands

Setpoint Integrated Solutions offers a variety of high performance and triple offset butterfly valves that will suit any application. We are proud to partner with Flowserve Durco and Triac brands. Contact us today to find out what configuration works best for you.

*This post was adapted from content created by VMA at their Valve Basics Course, found here.

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Continuing with the previous posts regarding Quarter-Turn Isolation Valves with a post about the characteristics of Butterfly Valves.  Like the Plug and Ball, the Butterfly Valve  saves weight and is faster to open and close, but it also saves space. * This article will focus on Resilient Seated design. There are also Double Offset and Triple Offset Butterfly Valves, which will be explored in a forthcoming post.

Butterfly Valves are designed so that the fluid is controlled by a disc, rather than a plug or ball, which helps save space.  It can have a resilient seating design. This design incorporates a disc that is held in the center of the valve and rotates to control product flow. The disc is always in the media stream with minimal flow restriction. Resilient seated butterfly valves are not ANSI‐rated but fit between ANSI Class 125 & Class 150 flanges.

Most butterfly valves use the same basic stem configuration as a trunnion‐mounted ball valve with a stem on the top and bottom. However, in this case the stem is mainly incorporated to balance the disc. Many different types of seat materials are available, including Buna (NBR), EPDM, Viton (FKM), PTFE, natural rubber or neoprene.

The seat shown above is a cartridge type seat; it has a phenolic backing ring with the elastomeric seating material molded to it. Other types of seats are booted and molded.
Both the cartridge and booted type seats can be replaced along with other critical parts.
Elastomers are excellent for a broad range of services, except steam.

There are a variety of butterfly valve styles based on how they are mounted in a piping system. The wafer style fits between two flanges and bolts surround the valve. The lug style has protruding lugs with tapped bolt holes mating it to standard flanges. The lug style butterfly valve is commonly used in dead‐end service. Both wafer and lug style valves do not need gaskets when mounting them in the piping. Then there is the flanged style. It has two end flanges and is bolted up just like any other flanged end valve. Another type is the grooved end butterfly valve. The grooved end design has a longer face to face, like the flanged, but is much faster to install.

The basic elastomer‐seated butterfly incorporates an interference fit where the disc diameter is slightly larger than the seat, which provides a bubble‐tight seal. The shut‐off capability is solely a function of this interference and greatly affects the torque. The primary stem seal is also an interference fit. With the improvement in elastomer technology and the introduction of many new elastomers, the performance of butterfly valves has improved. These butterfly valves are well suited for on/off and throttling applications. They are available in 2‐inch through 72‐inch sizes.

There are many materials that can be used for the body, stems, disc and seats. Some options for the body include various irons, bronze and steels. Stems are often made from 316 or 416 SS, and Monel. Discs use aluminum bronze, ductile iron or alloy 20, to name a few. We previously mentioned the most common elastomers. Take care when selecting the seat material. The user should be familiar with temperature limitations and compatibility of the elastomers for the intended service.

• Bodies:
  •  Ductile Iron
  • Cast Iron
  • Aluminum
  • Bronze
  • Carbon Steel
  • Aluminum
  • Stainless Steel
• Stems
  • 416 SS
  • 316 SS
  • Monel
• Discs
  •  316 SS
  • Monel
  • Aluminum
  • Bronze
  • Ductile Iron (NP)
  • Ductile Iron (PVF coated)
  • Alloy 20
  • Hastelloy C
• Seats
  •  Buna-N
  • Black Neoprene
  • Hypalon
  • Viton
  • Peroxide cured EPT
  • natural rubber
  • White Neoprene
  • ETM-30230
  • Fluorosteam
  • Peroxide-cured food grade EPT
  • Peroxidecured Buna-N
  • Sulfur cured food grade EPT

Butterfly Valves can be utilized in a variety of applications. The HVAC industry is one of the biggest users of butterfly valves. Other industries include chemical, petrochemical, refining, irrigation, and oil and gas drilling. Butterfly valves are also commonly found in food and beverage applications, water and wastewater, power generation, mining and dry bulk handling.

Setpoint Integrated Solutions offers a variety of butterfly valves that will suit any application. We are proud to partner with Flowserve Durco and Triac brands. Contact us today to find out what configuration works best for you.

*This post was adapted from content created by VMA at their Valve Basics Course, found here.