Offset Butterfly Valves: Zero, Double, Triple Compared | BVC

Zero, Double Or Triple Offset Butterfly Valve? What&#;s The Difference?

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Choosing the right valve is essential for a successful operation of any flow system that needs to control liquid flow. How do butterfly valves work and what differentiates them from each other you may be wondering? Each offset valve has functionality and benefits of their own. Read our blog to see which butterfly valve will aid in getting the job done!

Source: Crane Engineering

Triple Offset Butterfly Valves

Triple offset butterfly valves (TOV) have three separate offsets as shown in the picture above to the right. Two offsets are placed from the center while the third is on the seating surface which creates a cone type shape of the disc and seat. These valves are used mostly in applications where a tight bubble shut-off is required, a high temperature is expected or hard sealing surfaces are required with zero leakage(soft seat) or rated leakage(metal seat).

They are low maintenance with an extended valve life since there is no clogging or cavities between the sealing components and the disc only engages the seat in the last 1 degree. These valves are best for high-temperature gases and oils, as well as high pressure over 150 PSI or when API-607 Fire Safe is a requirement as TOV&#;s, are inherently Fire Safe T as well.

A triple offset butterfly valve is used in similar industries to those in which double offset valves would be used but are even more effective in demanding and tight applications. The TOV&#;s that offer the valve with the seat in the body vs seat on disc edge would last longer in abrasive applications. TOV with removable disc and stem without welding, (spline drive) will be more maintenance friendly.

Double Offset Butterfly Valves

This valve is also known as a high-performance butterfly valve and is quite popular since it can be used for various applications. This valve has two offsets from the center which creates a cam action during the application process. Double offset butterfly valves are best used for:

• Oil and gas
• Pulp and paper
• Power generation
• HVAC
• Chemical
• Shipbuilding
• Water/wastewater treatment

These valves are used for higher pressure than zero offset butterfly valves (ANSI Rated), and offer adjustable packing on the stem thus lower emissions and stem leakage.

Zero Offset Butterfly Valves &#;Concentric Design&#;

Zero offset butterfly valves are used for liquid and gas applications up to 400 degrees Fahrenheit and 250 PSI. The stem and disc of these valves are centered in the valve seat which is centered in the body of the valve. This valve can handle chemicals, coatings, food, some solids, and abrasive applications. An advantage of using a zero offset valve is that the media going through the valve will not contact the body since the seat of the valve covers the body.

Choosing the right valve for your operation can be a tough decision. Before making your purchase, contact our team of specialists at Butterfly Valves and Controls to help you find the valve that best suits your needs.

In recent years, metal-seated eccentric butterfly valves have competed with more traditional industrial valves like the globe and ball valves for critical applications. However, even though lots of people already know how a butterfly valve works, much of the confusion lies in how such eccentric valves differ and what applications are suitable for each. 

In this article, you are going to walk through the differences between these two kinds of butterfly valves to guide you when choosing a suitable industrial valve for your application.

What is a Double Offset Butterfly Valve 

The double eccentric offset butterfly valve can also be called the high-performance butterfly valve or double eccentric butterfly valve. This valve is suitable for thicker media that has a high pressure because its design does not allow too much contact with the disc and seat. 

Double Offset Butterfly Advantages

The balance of this valve is in the stem placed behind the circular disc. It allows the disc to self-adjust to the center, ensuring tight sealing. Even when the valve is fully opened, the valve does not touch the soft seat, ensuring a longer service life.

What is a Triple Offset Butterfly Valve 

Also known as the triple eccentric valve, the triple offset valve (TOV) has been around for more than 50 years. Initially designed to service water applications as a shutoff valve, TOV is now considered as a top choice for many critical process applications. 

The industrial valve sector, especially China butterfly valve manufacturers, are looking into the flexibility of these valves as alternatives to expensive and bulkier ones already in the market.  Recently, TOVs have been developed to deal with fugitive emissions control. 

Are you interested in learning more about 2-Offset Butterfly Valve? Contact us today to secure an expert consultation!

Triple Offset Butterfly Valve Advantages

As a butterfly valve, it also belongs to the quarter family. It is also lightweight and easy to operate. Installation is also a breeze since there is less pipe bracing needed. Replacement of seat rings is also easy as this valve is top-entry. 

The triple offset butterfly valve has a low torque so there is no need to have larger valves. That being said, this means higher savings costs. This valve has zero leakage closure on both ends. 

The introduction of soft seats increases the value of the valves. Aside from being fire-safe due to the metal seats underneath the soft ones, the valves can now self center because of the elastomeric seat material. 

Difference between the Double Offset and Triple Offset Butterfly Valve 

DescriptionDouble Offset Butterfly ValveTriple Offset Butterfly ValveSeat MaterialSoft MaterialMetal SeatSensitivity to Pressure and Temperature FluctuationsYesNoSeat FrictionLowVery LowClass RatingApplicationsProcess On/Off ThrottlingCritical and Severe ApplicationsSeat LifetimeLongVery LongFluide ServicesCleanDirtyBubble Tight OffYesYesPressure DropHighestHighestCostModerateHighest

One of the main differences between these two butterfly valves is how they look.  In the double offset butterfly valve, the two offsets of this kind of valve allow for easy opening yet retains its strong sealing power.
Configuration

The offset of the disc can be found in two areas:

1. Slightly on the right side of the valve centerline

2. Slightly near the center of the valve body where the stem is attached to the disc.

The first offset offers continuous sealing whereas the second offset allows the valve to open with little friction, increasing its life service. 

On the other hand, the triple offset butterfly valve is called as such because it has three offsets located in three different positions. These can be best understood if you check out the image below.

1. The center of the disc and seat 

2. In the centerline of the bore and attached to the stem

3. The offset is in centerline of the valve where it becomes the axis of the seat cone angle.

                                                              Source: http://www.valvemagazine.com 

The angled position of the disc in relation to the seats minimizes seat damage as well as preserve the integrity of the sealing surface. Additionally, it also reduces the chances of the valve sticking to the seats and it lowers operating torque.

Working Mechanism

As it is eccentric, the double offset butterfly valve disc moves away from the disc as it begins to open. To have an effective bubble-tight seal, this valve utilizes line pressure that acts against the disc.

The triple offset type does not act like a typical butterfly valve which, with a turn of a lever, moves sideways to allow entry of media, like a waving of a hand. The triple offset type acts like a globe valve where the disc moves somewhat like a cone, moving upwards to downwards. 

When the cone moves to become a circle, a tight seal happens. There is no drag when the seat takes contact with the disc because of the angled alignment of the disc in relation to the seat.

Contact us to discuss your requirements of Cast Steel Globe Valve-DIN. Our experienced sales team can help you identify the options that best suit your needs.