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.
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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.
Double-offset valves feature have two offset stems that offer especially long life due to reduced contact between valve, discs, and seats, and are known as high-performance butterfly valves. If your operations involve high pressures and particulate fluids, this type of valve can be especially useful. Apart from triple-offset butterfly valves, they are one of the most widely available eccentric-type butterfly valves on the market. They are also known as the 'elite' type of butterfly valves.
When compared to zero offset butterfly valves, double offset butterfly valves can withstand higher pressures. They're made of Hastelloy, stainless steel, carbon steel, and other materials with ANSI Class ratings of up to 600. Their rigid Polytetrafluoroethylene (PTFE) seats (ANSI class butterfly valve) are usually made of Teflon and come in Fire Safe designs with metal seats as backups.
A two-offset disc can be used up to 1,480 psi [10 MPa] in double-offset butterfly valves. Unlike the single-offset design, the stem of the double-offset butterfly valve is located behind the disc. The second offset stem is pushed to one side from the middle of the disc in the high-performance butterfly valve. Because of the offset geometry, the disc can be rubbed over the seat with only 1° to 3° of 90° rotation. The cone profile while sealing the valve is the action of the double offset butterfly valve. The configuration of the disc and shaft offsets creates the cam action of the disc in the seat, which reduces the torque required to operate the valve.
Double Offset Butterfly Valve
With the triple offset butterfly valve there are three offsets. Two are placed in a similar position to the double offset butterfly valve, while the third offset is the geometry of the seating surface, creating a type of cone shape of the disc and seat. This cone angle, along with the two eccentric shaft offsets, allows the disc to seal against the seat with no friction.
This seat design also allows for uniform sealing, and thus a tight shutoff in a metal seat design. This design is a lower cost, lower torque option (easier to automate), than alternative style metal seated valves.
Triple offsets are generally used in applications similar to gate valves, where a metal seat is required, and tight shutoff and/or quarter turn actuation is desired. Applications like high pressure steam (over 150 PSI), superheated- steam, high temperature gases and oils, high temperature applications are good for this type of valve because a metal seat is required over a soft seat.
The triple offset valve is used in similar industries as the double offset butterfly valve, but in more demanding applications.
Triple Offset Butterfly Valve
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.
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.
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.
Commonly, double offset butterfly valve seats are made of plastic or elastomeric material like PTFE. To use this kind of valve in high-temperature applications, the metal seat design is utilized but this needs to meet standard specifications of API 607.
Double offset butterfly valves are can reach pressure ratings up to ANSI Class 600. These can be made from carbon steel, stainless steel or Hastelloy with an elastomeric material such as Teflon.
The nature of media with which these valves operate dictates what materials to use for the valves. Triple offset butterfly valves deal with corrosive media so the valve often has metal seats made from high-grade materials such as stainless steel or duplex steel.
The triple offset butterfly valve can also have double seat type design, that is, an elastomeric or graphite material covers a stainless steel seat. Often, the seats of this valve are field replaceable. This should only be employed in cases where media is not abrasive or has a high temperature.
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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.
Double offset butterfly valves can often be found in large underground water applications. You can often see these valves with gate valves since both operate in the same. These are best used when you need to have the highest degree of tight sealing.
Often, you can find double offset butterfly valves in oil and gas applications, HVAC, waste and wastewater treatment facilities and Shipbuilding factories.
Triple offset butterfly valves are efficient in applications that have special challenges such as the abrasive material, high pressure or temperature and even those that are prone to fugitive emissions.
You would find triple offset butterfly valves in applications such as steam with over 150 psi or high-temperature pure gas or liquid. In cases like these, the metal seat types without the soft coating are more economical.
These valves are often used in industries such as oil and gas processing, refining, chemical and petrochemical applications, power generation, offshore applications, pulp and paper, and so on.
Between the double offset and the triple offset butterfly valve, if your primary concern is to have bubble-tight sealing, choose the double eccentric butterfly valve. If the application is highly corrosive, abrasive or deals with high pressure and temperature, the triple eccentric butterfly valve is worth considering.
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When it comes to butterfly valves, there are two main types: double offset and triple offset. The question of whether to use a double offset or triple offset butterfly valve is one that is often debated in the engineering world. Both types of valves have pros and cons, and the decision ultimately comes down to the specific application. In this blog post, we'll explore the key differences between double offset vs triple offset butterfly valve and help decide which is the right choice for the project.
A double offset butterfly valve is a quarter-turn valve that uses a disc to control the flow of fluid. The disc is connected to a rod attached to a lever, and when the lever is turned, the disc rotates to open or close the valve. It means that the disk is not in line with the flow of the fluid. This allows for more precise control of the flow. Double offset butterfly valves are used in various industries, including oil and gas, chemical, and power generation, where a high degree of control is required.
Butterfly valves are frequently used in industrial applications because they offer many advantages over other valve, such as gate and ball valves types. In this article, we will explore five advantages of double offset butterfly valves:
While the double offset butterfly valve has many advantages, there are also a few disadvantages. Here are five of the most significant disadvantages of this type of valve:
In the world of valves, the triple offset butterfly valve is a specialized type of valve often used in high-pressure and high-temperature applications. Triple offset butterfly valves have three sealing surfaces instead of the usual two, which gives them a tight seal that can withstand high pressures. These valves are also often used in situations where a standard butterfly valve cannot provide a proper seal, such as in high-temperature applications.
While triple offset butterfly valves are more expensive than regular butterfly valves, they are often worth the investment due to their ability to provide a tight seal under challenging situations. For a high-pressure or high-temperature application, a triple offset butterfly valve may be the right choice.
One type of valve that has become increasingly popular in recent years is the triple offset butterfly valve. This valve offers several advantages over other types of valves, including the following:
A triple offset butterfly valve (TOFV) is a type of butterfly valve that is designed to provide a tight seal even after extended periods of use. The valve gets its name from the three different offsets used in its construction: an offset in the body, an offset in the disc, and an offset in the seat. While a TOFV can provide many benefits, some potential disadvantages should be considered before using one. Here are five potential disadvantages of a TOFV:
One of the most important decisions one can make when choosing a butterfly valve is deciding between a double offset and triple offset butterfly valve. Both valves have advantages and disadvantages, so it is essential to understand their critical differences before deciding.
Here are the key differences between double eccentric vs triple eccentric butterfly valve:
When it comes to butterfly valves, there are a few factors that need to take into account to ensure when choosing the best possible options to the needs. Here are five factors to keep in mind when selecting a butterfly valve:
The pressure rating of a butterfly valve is an essential factor to consider, as it will determine the maximum pressure the valve can withstand. Make sure to choose a valve with a pressure rating that meets or exceeds the operating pressure of the system.
The temperature rating of a butterfly valve is also an essential factor to consider, as it will determine the maximum temperature the valve can withstand. Make sure to choose a valve with a temperature rating that meets or exceeds the operating temperature of the system.
When choosing a butterfly valve, it is essential first to consider the materials from which the valve is made. The material of the valve will dictate how well the valve performs and how long it lasts. Some materials are better suited for specific applications than others. For example, a butterfly valve made from stainless steel will be more corrosion-resistant than one made from plastic. It is also essential to consider the compatibility of the materials. Ensure that the materials of the valve are compatible with the fluids or gases flowing through it. If the materials are incompatible, the valve may not work as intended or be damaged.
Understanding the fluid that flows through the application before purchasing valves is essential. How well the valve seals will be affected by the type of fluid. For gas media, butterfly valves must have a specified minimum leakage pace at a particular operational pressure and temperature. The liquid media valve must have a tight seal to control liquid leakage.
Solids valves should have a seal that fits flush into the pipe. This will prevent obstructions to the flow and keep materials from accumulating in the valve. Solids can also wear down valve seats faster than other materials. Dry materials may get stuck between the seat and the disc, and larger valves are better suited for solid media.
A pressure drop indicates a system's energy loss and can cause problems downstream. The pressure drop can be caused by the butterfly valve itself or other system factors, such as the piping or fittings. The pressure drop is an essential factor to consider when selecting a butterfly valve, as it can impact the valve's overall performance. A high-pressure drop can cause the valve to fail to close properly, while a low-pressure drop can cause the valve to leak. The pressure drop should be listed in the specifications for the valve, so be sure to check before making the purchase.
When evaluating butterfly valves, one of the most important factors is the valve speed of operation. The speed of operation is a measure of how quickly the valve can open or close. It is essential to choose a valve with a speed of operation that is appropriate for the application. If the valve is too slow, it may not be able to keep up with the flow demand. If the valve is too fast, it may cause turbulence and chaos in the system. The superior speed of operation for a butterfly valve is typically between 0.5 and 2 seconds.
There are many factors to consider when choosing between a double offset and a triple offset butterfly valve. The most important factor is the application in which the valve will be used. If the application requires a higher degree of precision, then a triple offset butterfly valve may be the better choice. If the application is less demanding, then a double offset butterfly valve may suffice.
Double offset butterfly valves are more commonly used because they provide a better seal and are less likely to leak. They are also easier to maintain and repair. However, they are not as well suited for high-pressure applications.
Triple offset butterfly valves are less common, but they are better suited for high-pressure applications. They provide a tighter seal and are less likely to leak. However, they are more difficult to maintain and repair.
So, which type of butterfly valve is right for you? It all depends on your specific application.
In conclusion, double offset and triple offset butterfly valves are excellent choices for various applications. Double offset valves have a lower initial cost and are easier to maintain, while triple offset valves provide superior performance and are more durable. Ultimately, the best choice for a particular application depends on the project's specific needs. Contact the best industrial valves manufacturers for purchasing the reliable butterfly valve for all industrial uses.
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