A butterfly valve is a common type of industrial valve. It uses a butterfly-like round disc to control the flow. A butterfly valve is able to control liquid flow through a pipe without any significant impact on the other side.
If you are looking for more details, kindly visit double offset vs triple offset butterfly valve.
A butterfly valve is designed to be a highly efficient option when controlling flow through a pipeline, which saves both time and money. Its benefits make it a highly preferred choice in many applications.
There are different types of butterfly valves available in the market. The two most common types are double offset and triple offset butterfly valves. The main difference between a double-offset and a triple-offset butterfly valve is their structure. In double-offset models, the stem and disc deviate from their center. This results in less scraping and over-compression, which increases the valve&#;s lifetime.
If you want to know more about the difference between double offset and triple offset butterfly valves, continue reading this article.
What is Double Offset Butterfly Valve?A double offset butterfly valve is characterized by two counterbalance contrasts. The first offset is near the center of the valve body, where the stem attaches. This offset allows the valve to seal without any friction, while the second offset allows the valve to open with minimal friction. This means that it can be used for a variety of applications.
A double offset butterfly valve differs from a symmetric butterfly valve in two major ways. The first is the disc itself. The disc is shaped like an oval, while the second is parallel to the flow. The disc is also deformed in a unique way. Its asymmetric shape enables it to reduce pressure loss while reducing seat wear. In addition, it is able to accommodate multiple operating modes.
Pros and Cons of a Double Offset Butterfly Valve Pros of Double Offset Butterfly Valve Reduced Wear and TearThe design of the double offset butterfly valve significantly reduces wear and tear on the valve seat and disc.
The offset shaft and cone-shaped sealing mechanism allow for a tight seal with minimal friction during operation, contributing to increased durability.
Lower Operating TorqueCompared to the traditional butterfly valve, the double offset design requires lower operating torque.
This means that the valve can be easily and efficiently actuated, making it suitable for applications where lower torque requirements are advantageous.
Extended Service LifeThe reduced friction and wear, combined with lower operating torque, contribute to an extended service life for double-offset butterfly valves.
This makes them a cost-effective choice in the long run, as they require less frequent maintenance and replacement.
Enhanced Sealing PerformanceThe double offset configuration improves the sealing performance of the valve.
The offset shaft allows the disc to move away from the seat rapidly during the initial opening, minimizing contact and reducing wear.
This results in improved sealing integrity over time.
Versatility in ApplicationsDouble offset butterfly valves are versatile and find applications in various industries, including oil and gas, petrochemical, water treatment, and more.
Their ability to handle high pressures and temperatures makes them suitable for diverse operating conditions.
Cons of Double Offset Butterfly Valve CostDouble-offset butterfly valves can be more expensive upfront compared to traditional butterfly valves.
The advanced design and materials used in manufacturing contribute to a higher initial cost.
However, this cost may be justified by the long-term benefits.
Complex DesignThe double-offset butterfly valve has a more complex design than the standard butterfly valve.
The additional features, such as the offset shaft and cone-shaped sealing mechanism, may require more intricate manufacturing processes, potentially increasing maintenance complexities.
Limited to Certain SizesWhile suitable for various applications, double-offset butterfly valves are more commonly available in larger sizes.
This limitation may affect their use in smaller pipelines or applications where space is a constraint.
Sensitive to ContaminantsThe precision required for the sealing mechanism makes double-offset butterfly valves sensitive to contaminants in the fluid.
Particles or debris in the flow may impact the sealing performance, requiring proper filtration and maintenance.
Potential for CavitationIn certain conditions, double-offset butterfly valves may be susceptible to cavitation, especially during rapid changes in flow.
Cavitation can lead to erosion and damage to valve components, necessitating careful consideration of operating conditions.
What is Triple Offset Butterfly Valve?The triple name offset indicates that the disc is not vertically centered and slopes up and down. As a result, it appears to be off-balance. The stem connects the disc to the valve body and, in turn, creates a third offset, which is the stem&#;s thickness from the flat side to a rounded tip. Because of this, the triple offset butterfly valve has a lower maximum capacity than a flat disc valve.
The triple offset butterfly valve is an effective, high-pressure valve that has many benefits. Its design features a metal-to-metal sealing arrangement that virtually eliminates disc-to-seat rubbing, which causes wear and a shorter life span. A triple offset butterfly valve is a high-performance valve that closes with zero leakage. The offset angle eliminates rubbing between the seat ring and the seal, which results in a repeatable, zero leak shutoff.
Pros and Cons of Triple Offset Butterfly Valve Pros of Triple Offset Butterfly Valve Bubble-Tight SealingThe triple offset design provides bubble-tight sealing, ensuring a complete and tight closure of the valve.
This is particularly advantageous in applications where leakage prevention is critical, such as in high-pressure or hazardous fluid environments.
Minimal Wear and TearThe continuous contact-less rotation and seating characteristic of the triple offset design result in minimal wear and tear.
This leads to an extended service life and reduced maintenance requirements, making it a cost-effective choice in the long run.
High-Temperature ResistanceTriple offset butterfly valves are suitable for high-temperature applications due to the use of materials that can withstand elevated temperatures.
This makes them ideal for industries such as petrochemical, refining, and power generation.
Bi-Directional SealingThe triple offset design allows for bidirectional sealing, meaning the valve can provide effective closure regardless of the flow direction.
This feature enhances the versatility of the valve and ensures reliable performance in varied operating conditions.
Reduced Torque RequirementCompared to traditional butterfly valves, triple offset designs generally require lower torque for operation.
This contributes to efficient actuation and ease of use, especially in large-sized valves.
Cons of Triple Offset Butterfly Valves Higher Initial CostTriple offset butterfly valves tend to have a higher upfront cost compared to traditional butterfly valves.
The advanced design, precision manufacturing, and high-quality materials contribute to this increased cost.
However, the long-term benefits may justify the initial investment.
Complex Design and ManufacturingThe intricate design of triple offset butterfly valves, including the conical seating, requires precision manufacturing.
This complexity can lead to higher production costs and potentially longer lead times for procurement.
Sensitivity to ContaminantsThe precision required for the triple offset design makes these valves sensitive to contaminants in the fluid.
Foreign particles in the flow can affect the sealing mechanism, emphasizing the need for proper filtration and maintenance.
For more double seat valveinformation, please contact us. We will provide professional answers.
Limited to Certain SizesWhile available in various sizes, triple-offset butterfly valves are more commonly used in larger applications.
This limitation may impact their use in smaller pipelines or systems where space constraints are a consideration.
Specialized ApplicationsTriple offset butterfly valves are often chosen for applications where bubble-tight sealing, high temperatures, and bidirectional capabilities are critical.
However, for less demanding applications, the additional features may not be necessary, making them potentially over-engineered.
Difference between Double Offset and Triple Offset Butterfly ValveThe main difference between double offset and triple offset butterfly valves is in the seat material. While double offset valves have soft seating material, triple offset comes with a metal seat. Another difference is pressure sensitivity and temperature fluctuations. Double offset valves are sensitive to pressure and temperature, but triple offset valves are not sensitive.
The Double Offset Butterfly Valve is better suited for bubble-tight sealing, while the triple offset butterfly valve is better suited for high temperatures, high pressure, and abrasive media. In addition, this valve has a high sealing surface and requires less maintenance. It also offers longer life than the double offset butterfly valve, which makes it ideal for applications involving high temperatures or corrosive media.
The differences between the double offset butterfly and the triple offset butterfly valve are significant. In addition, the metal seats of triple-offset valves can accommodate higher pressures than double-offset versions and require less torque. While the double-flanged butterfly valves are less expensive than triple-offset varieties, they are not ideal for high-pressure applications and unusual materials.
Double offset valves have low seat friction, whereas triple offset valves have very low friction. The seat is triple offset valves last longer than the double offset seat. Triple offset valves are often used in severe and critical applications, while double offset valves are used for on, off, and throttling functions.
About Xintai: Your Reliable Valve ManufacturerXINTAI Valve Group Co., Ltd., established in , stands as a prominent force in the valve manufacturing industry, seamlessly integrating research and development, casting, production, and sales.
Situated in the Longwan Konggang New District of Wenzhou, the group boasts cutting-edge technologies and operates from four manufacturing bases, equipped with eight advanced casting production lines.
Their expansive 32,000 square meters workshop houses modern facilities, including R & D centers and operational hubs.
With an impressive annual production exceeding 270,000 valves since the inception of their casting factory in , XINTAI has established itself as one of the largest manufacturers of casting valves in Wenzhou.
The company&#;s commitment to quality is evident through its ISO certification, domestic TS security certification, CE, OHSAS, and API certifications, ensuring accredited quality and adherence to industry standards.
XINTAI Valve Group takes pride in its leading forging process, crafting valves with exceptional strength suitable for systems with high-pressure and high-temperature requirements.
The company provides custom valve solutions, offering a comprehensive range of valve products, including the following:
With three strategically positioned offices, two marketing centers, and an inspection center, XINTAI Valve Group continues to be a trusted name in the industrial valve manufacturing sector, delivering reliable and innovative solutions to industries globally.
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Butterfly valve design: conc, ecc, doubl ecc or triple eccentric?
5
thread408- Forum Search FAQs Links MVPsForum
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(Industrial)
(OP)
19 Jan 06 03:37Hello,
Is there somebody how really knows the different (dis)advantages (when and where to use wich type?) of the different butterfly valves designs, offset.
Specially the differnece between single and double eccentric is a bit of a mystery for me. Has it something to do with selingforces (moments?) or gives double eccentric less friction, ....?
Thanks
greetings, Pieter
4
JimCasey(Mechanical)
19 Jan 06 10:24The non-offset valves are the low end of the spectrum. They are generally "rubber" lined. Typically capable of sealing to 150 psi, temp-limited by the elastomer of the seats, and the shaft seals by interference fit between the shaft and liner. These can work on dry granular solids, or with a polished vane and pedigreed liner they are used on food-or pharmaceutical applications. As the valve opens and closes, some part of the vane is always wiping the seat, causing friction and wear. These valves are position-seated, When the vane is at 90-degrees to the pipe centerline, they are as closed as they get.
I don't think there IS a single-offset valve, but if I am wrong someone will tell me soon.
Double-offset valves, also known as high-performance butterfly valves, have the shaft mounted slightly offset from the pipe centerline, and the shaft is mounted behind the sealing band of the seat. The seat is a narrow resilient band is clamped in the body and must be resilient. PTFE is resilient enough to seal, and the disc only wipes the seat for a few degrees of travel at seating. So there is a lot less friction, the seats can last longer, and the seats can be made from materials that are capable of dealing with higher temperatures than the rubber seats of the lined valve. Metal seats are available for HP Butterfly valves allowing operation to around F. SInce the disc is offset from the shaft, there is a lot of metal in the flow stream in the wide-open position, and double-offset valves have somewhat less maximum capacity than flat-disc, non-offset valves. These valves are also position-seated. Unlike the lined valves, these valves can actually damage the seats if they are overstroked so they almost all have a travel-stop pin in the body.
Triple offset valves are set up much like double-offset valves, except that the profile of the outside diameter of the vane is machined as a conic section. The cone would be projected upstream, tilted along the edge of the pipe wall on the leading edge of the disc. The cone is not centered in the pipe-hence the third "offset". What this does is to allow seating without rubbing, and the seats hardly have to be resilient at all. SO once the valve is comanded to move, there is no breakaway torque, the running torque is essentially just packing friction, and even the dynamic torque produced by the flowing media over the vane is low. I said the seats are hardly resilient: Ususally the seats are something like a stack of thin stainless sheets bonded with graphite, so they can deform slightly and conform to the seating surfaces. Triple offset valves are not positon-seated-they are torque-seated. When the disc hits the seat it is metal-to-metal contact and they cannot be overstroked. But to get tight shutoff, it is necessary for the actuator to lean on them mightily to squeeze the seating surfaces together. SO a triple offset can give you tight shutoff at elevated temperatures, there are no soft elastomers/polymers to be damaged by particles or velocity effects, and they work pretty well for control.
If you paid attention in geometry class you will remember that an angled slice through a cone is not a circle but an ellipse. That's right-the seats and vane are NOT ROUND. As long as there is a good SPC/ISO manufacturing plan the pieces are interchangeable, so repair parts will still fit.
Search the web for Bray or Keystone for the rubber-lined valves, search for the Flowserve BX or the Keystone K-Lok for the double-offset valve, or the Tyco Vanessa or Tri-Centric for the triple offset valve.
(Petroleum)
19 Jan 06 11:58If you google TRICENTRIC and WEIR, they have a great little paper that explains all of this, and great illustrations too.
I can't insert the diagram here, but here is the description of the 3 offsets.
Tricentric® Sealing System
TRIPLE OFFSET
Offset #1 The shaft is positioned forward of the valve
seat providing an uninterrupted seating surface.
Offset #2 Centerline of disc rotation is located away
from the centerline of the seat allowing the seal to lift
off and away from the seat on opening.
Offset #3 The cone axis is offset from the centerline
of the seal to provide a conical sealing surface that
allows the seal to rotate in and out of the seat without
interference, sliding or jamming.
(Petroleum)
19 Jan 06 12:06Jim,
You can buy a single offset disc valve. Many are going to double and triple offset due to better sealing, as you mentioned above. Many others, like me, are going to other valve types as costs are coming down.
Great descriptions by the way!
(Petroleum)
19 Jan 06 13:19Asereng,
could you please post the link for that paper here. I tried to google it but "it was not found"
Thanks
(Petroleum)
19 Jan 06 13:28 http://www.weirvalve.com/weir/valves/home.nsf/Page/DownloadsProduct_literatureButterfly_ValvesThe PDF is titled "Tricentric Butterfly Valve".
(Petroleum)
19 Jan 06 13:30khan101,
You are buying the beers the next time I see you in the field.
(Mechanical)
19 Jan 06 22:31Jim,
Your explaination is so detailed. I learned much from you on valves. In fact, I work as distributor, one of my clients complain the triple offset valve need to have a larger torque to have a bubble-tight, compared with double-offset. Do you have any idea how to reduce the torque? Thanks a lot
(Mechanical)
20 Jan 06 08:59Geosmith: The torque is needed to cause the seating surfaces of the Triple Offset Butterfly (TOB) to deform enough to seal. Using a soft seat would require less torque, if you can give up some margin on the pressure/temperature limits.
Most of the time, the triple offset is used for isolation in lieu of a gate valve. THe Tyco Vanessa valve is actually marketed as a Quarter-Turn Gate (QTG). Gate valves need gorilla seating loads, don't really shut off all that tight, and are a LOT taller than an equivalent TOB valve. The TOB valve might cost a little more but it saves you a lot of room in a pipe chase, shuts off tight, and has substantially less lifetime environmental leakage, too. The only real offsetting features are that with the vane and shaft in the flowstream, the capacity of the TOB is somewhat less that the gate valve, and the gate valve is piggable.
(Petroleum)
20 Jan 06 10:19GeoSmithAnother alternative to the TOB is the slab gate valve. The gate sort of looks like a spectable blind - the orifice moves up and down.Here is are a couple of links with a good picture:Instead of a traditional knife or wedge type gate valve, which may be prone to gunk in the channel, causing sealing problems, this type has a full plate that moves an orifice/solid blind in and out of the flow path. Because the orifice slides completely out of the flow path (versus a knife coming into a seat), there is better sealing as the seats are parallel to the movement of the sliding plate.This type of valve gives you:- lower seating loads (don't need "gorilla" torgque)- very good shutoff classifications (API 6A)- high working pressures- bi directional sealing
(Mechanical)
20 Jan 06 11:21face-to-face
dimension only (and not to torque requirements), in order to distinguish the valves with an "extended" length in the pipe axis direction, intended to replace gate valves in existing plants.All
:GeoSmith,where is the seating element of the tripple-offset valves you are talking about? Is it a flexible ring bolted to the disc (against an hardened seat surface on the body) or is it fixed to the body?This may affect the torque requirements of the valve... (in any case, usually the most "critical" are the opening ones,the torque needed to unseat the valve).JimCasey,I think that the "Quarter-Turn Gate (QTG)" denomination once used byrefers todimension only (and not to torque requirements), in order to distinguish the valves with an "extended" length in the pipe axis direction, intended to replace gate valves in existing plants.(See, for example: http://www.vanessavalves.it/series3-1.htm#ppp , 5paragraph after the table...).Tothere are a lot of discussions already written about this issue, maybe you'll find useful to take also a look at thread408- andwithin this Forum...!Hope this helps,
(Mechanical)
23 Jan 06 20:56If you really need to get to some high seating forces without huge torque and breakaway, see Trunion valve...Has some shortcomings compared to pivoting disk valves, but has some distinct advantages too.
(Mechanical)
24 Jan 06 10:14Anegri,
The QTG DOES, In fact, have a body with the same face-to-face as a gate valve. My point was, if a user is distressed by the torque required by triple-offset a butterfly valve, he will not be relieved by going to alternative technology gate valves. We could do paragraphs about solid wedge, flex wedge, double-disc-parallel seat types of gate valves, but in every case you have to drop them into the seated position then lean on them enthusiatically to get them to seal well.
Ashereng's slab gate is a valve to consider. It would be a position-seated valve. It is less environmentally friendly because of the long stroke of the stem thru the packing, makes for a tall assembly, and usually slab gates (conduit gates) have soft seats with the inherent benefits and disadvantages thereof. But they are truly obstructionless in the Wide-open position.
If you have not yet engraved your granite slab, please grab one and chisel in the following thought:
There is a best valve for every application.
(Mechanical)
27 Jan 06 00:24Thanks for all suggestions for the high torque required for triple offset valve. On the other hand, my client found out and complain to me that the screws in the ring (seat retainer) are not strong enough to hold the seal. What can I do? Any formula to calculate the sizes or number of cap screws are strong enough to hold the pressures? I think we need to change the manufacturers. So bad!!!
(Mechanical)
27 Jan 06 10:03The screws in the seat ring retainer are only there to maintain assembly before the valve is installed. After you squash it between two flanges and torque a large number of large bolts down on it, it ain't going anywhere. Exception: Lugged valve for end-of-line service. Solution: Bolt it in place with a flange anyway. Here where I work, the retainer for our HPBVs is just snapped in place with a Viton o-ring. This gives an uninterrupted gasket surface, and it's easy to pop out the retainer to replace the seal. The o-ring is NOT for sealing, and the valve is not rated for unsupported end-of-line service.
MOST triple offset valves have a fixed seat in the body and the conformal seal in the disc, held in place with a lot of smallish screws and a relatively beefy ring.
(Mechanical)
30 Jan 06 02:29GeoSmith,simply contact the triple offset valve Manufacturer: they should have, of course, design calculations good to demonstrate that the retainer flange bolts will withstand the service conditions.Otherwise (if you can't get replies about this issue)... switch to a more serious Manufacturer!!(See for example the ones mentioned in thread408- ...)Hope this helps,
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