What Is The Difference Between Double And Triple Offset Butterfly Valves

Most people already know how a butterfly works. The point of confusion comes in knowing how a double offset valve differs from a triple offset valve. Furthermore, which application each is best suited for. As one of the leading butterfly valve manufacturers in Indonesia, we are uniquely suited to clear this confusion. So, in this blog, we will walk you through both types of butterfly valves and what makes them different.

What Is A Double Offset And A Triple Offset Butterfly Valve?

A double offset butterfly is a high-performance valve. It is ideal for thicker media since the disc and the seat doesn’t have much contact. Thus, they can withstand high pressure.

Also called double eccentric butterfly valves, the stem is placed behind the disc for balance. This enables the disc to self-adjust, creating a tighter seal. They have a long service life because even when completely open, the valve doesn’t come in contact with the soft seat.

A triple offset butterfly valve was initially made as a shut-off valve for water services. Also called a triple eccentric valve, they are now best suited for critical processes and fugitive emissions control. They are the ideal alternative to bulkier and more expensive valves.

Also Read : Everything About Automating Butterfly Valves?

Belonging to the quarter valve family, they are easy to operate. Installing them is simple because minimal pipe bracing is necessary. Lightweight and top-entry, replacing their seat rings is an easy task. Furthermore, they have low torque, which means larger valves are not needed. They also come with zero leakage closers and metal seats under the soft seat. The elastomeric seat makes them fire-safe.

How Do The Two Butterfly Valves Differ?

The biggest difference between a double offset and triple offset butterfly valve is their appearance.

In double butterfly valves, the two offsets are:

A little to the right side of the centreline.
Near the valve’s centre, where the disc and stem are attached.

The two offsets make it easy to open the valve while ensuring the sealing power is robust. This happens because the first offset delivers a continuous seal. The second one reduces friction when opening the valve. It also increases the lifespan of the valve.

In a triple offset butterfly valve, the 3 offsets are:

At the middle of the seat and disc.
Attached to the stem and right at the centre line of the bore.
The axis of the seat cone at the centre of the valve.

This valve has minimum seat damage because the disc is at an angled position to the seats. The position also helps maintain the integrity of the seal. Additionally, the operating torque gets lowered, and the valve doesn’t stick to the seat.

Blue with yellow colour valve installed by triple offset butterfly valve manufacturers in Indonesia

So, the question now is which type of valve to use for your application. The rule of thumb is if the most important factor is to achieve a bubble-tight sealing, then the double offset is the right choice. In case the application deals with high temperatures, corrosive media, extreme pressure or abrasive material, then the triple butterfly valve is the way to go.

The second difference is in their working mechanism.

When the double butterfly valve opens, it moves away from the disc. It makes use of line pressure against the disc to ensure a tight and effective seal. On the other hand, the triple offset valve works, unlike a standard butterfly valve.

Butterfly valves move sideways when the lever is turned, allowing the flow of media. A triple offset moves like a globe valve. The disc moves upwards and downwards like a cone.

The seal occurs when the cone moves into the circle position. Since the seat and disc have an angled alignment, there is no drag when the two come in contact.

Where Can You Use The Two Valves In Indonesia?

Another difference between double and triple offset butterfly valves is in their applications. Large underground water applications often utilise double type valves. They are usually installed along with gate valves. They are also useful when the degree of tight sealing required is high.
Other industries and niches where you can use double offset butterfly valves include:

Oil
Gas
HVAC
Shipbuilding
Wastewater facilities
Waste treatment plants

Whereas triple offset type of valves is beneficial where the application has unique challenges. For instance, the material is abrasive, or the temperatures are too high. They are also applicable in high-pressure environments and where fugitive emissions may happen.

You can install them in pipes transporting a pure gas or liquid at over 150 psi. This is possible because the seat is made of metal and has no soft coating. Some sectors where you can utilise triple butterfly valves include:

Oil
Refining
Chemicals
Gas processing
Pulp and paper
Petrochemicals
Power generation
Offshore applications

Your Takeaway:

There are plenty of differences between the two kinds of butterfly valves. For instance, the material they are made of varies. Because triple eccentric valves operate in corrosive media, they are made of duplex steel or stainless steel. The high-grade material ensures they last longer. Double offset valves have seats made of an elastomeric material such as PTFE or Teflon.

The point is that knowing the differences can help you understand which application they are best suited for. But since they vary so much, it is a challenge to dive deep. Our advice is to talk to industrial valve manufacturers in Indonesia. They have the expertise to allow you to make an informed decision. Their knowledge can guide you on every kind of butterfly valve and which benefits your industry and application the most.