Double Offset Butterfly Valve

Product Details

DOUBLE OFFSET BUTTERFLY VALVE

Industrial valves require a broader pressure and temperature range than traditional butterfly valves could achieve. This has led to the development of a high-performance butterfly valve. Double eccentric butterfly valves provide a simple, lightweight, compact and cost-effective structure with a low operating torque benefit.

What is Double Offset Butterfly valve?

High-Performance Butterfly Valves uses a disk offset from the centre of its seat, due to which it is named as Double Offset butterfly valve. In this setting, the disk is eccentric or offset from the seat of the valve. When the disk begins to rotate, it shifts away from the seat instead of around it. In fact, this design utilizes line pressure to help give it a proper sealing. This functionality allows the usage of double offset butterfly valves in high-pressure systems such as ethanol or HVAC. PTFE or plastic are used commonly as a seat material in double offset valves, but metal seats are also provided to meet fire-testing requirements such as API 607.

Double offset butterfly valves are commonly regarded as high-performance butterfly valves. They are among the most popular eccentric butterfly valves in the market, apart from triple-offset valves. Additionally, they have often considered the finest type of butterfly valves.

Description

- Butterfly valves resilient-seated butterfly valves provide up to 50,000 bi-directional, gas-tight shutoff cycles and are available in standard pressure ratings from 230 psig to 250 psig test.

- Butterfly valves have an ISO-5211 stem and gasket, allowing the use of anyone's ISO-5211 actuator. Most manufacturers use only ISO gaskets and special stems that do not fit standard ISO-5211 actuators.

- The valve disc is investment cast and utilizes reinforced vanes to reduce pressure drop and increase allowable pressure. The disc edge is flat, allowing the disc to slide over the seat rather than pushing through it. A reduced diameter flap available for 87 psig shutoff is used to reduce pressure and extend seat life.

- Shaft is pinless in the flow stream and uses splined connections within the disc to maintain a consistent large stem diameter at all times. 14 in. and larger valves have a splined split shaft design.

- 3 Bearings are located above and below the valve seat to stabilize the shaft. The bottom bearing is bronze with optional stainless steel bearings, and the bearing above the seat is standard stainless steel. The top of the pad is a Delrin thrust bearing and O-ring

- Many users use the optional Nylon 11 coated body in severe conditions or, in the case of salt water, a Nylon 11 coated 316 stainless steel disc to avoid crevice corrosion.

- Stem retainers have one of the best systems available. The stem is held in place by a stainless steel pin that allows fluid to flow over the top of the shaft and rotate in a groove machined into the top mounting pad. The stem, which is isolated from the media, is easily removed.

- Butterfly valve body is standard CI round piece (except 8-12", which is ductile iron)

- All lug bodies are standard ductile iron.

- All VF-7s are one-piece bodies cast in 304 stainless steel and 316 stainless steel.

- All VF-7's are ABS type approved for marine service

- A variety of seats are available such as EPDM, White EPDM, Buna N, Viton, Viton for Steam, Silicone and Neoprene. EPDM and Buna seats are FDA approved for food service. This series is approved for NSF-61 potable water service.

- Operators include top trigger, bottom trigger 10 position, or flip-up notch plate to infinite position. Iron and stainless steel gears with or without sprocket operator. All handles are lockable and gears can be locked with locking attachments.

 

Features.

- Valve body styles: clip-on, lug, and double flange

- Body materials: cast iron, ductile iron, nylon 11-coated cast iron or ductile iron, carbon steel, 304 and 316SS

- Body coating: standard two-part polyester epoxy, optional nylon 11

- Discs: Nylon 11 coated ductile iron, 304SS, 316SS, aluminum bronze, nylon 11 coated 316SS

- Seat: EPDM (food grade), Buna N, Viton, white EPT (food grade), Hypalon, silicone, neoprene

- Bearings: lower stem bronze or (optional) SS, upper (seated) SS, top Delrin

- Stem: 410SS, 304SS, 316SS, 17-4 Ph SS

- Mounting: ISO-5211 stem (small square) and mounting pad

- Drive: 14" one-piece shaft, splined to disk attachment (VF7A), split shaft > 0" with splined drive (VF7A)

- Stem Retention: 1.5" to 12.0" Q-pin slots in top gasket to retain SS through pins, 14.0" to 48" and all stainless steel valves have removable plates to retain SS through pins

- Working pressures: 87 psig, 150 psig, 230 psig Two-way gas-tight shutoff

- 5"-12.0" lug rated 200 psig dead shutoff, 14.0" and above lug rated 150 psig dead shutoff, test reports available

- Private label valves available

 

 

Specifications.

- End connections: 125/150 ANSI, butt clamps, lugs, flanges

- Wall thickness: ASME B16.34, AWWA C504

- Installation: ISO-5211 (for all ISO-5211 operators)

- Design: ISO-5208, AWWA C504, ASME B16.34

- Face-to-face: API-609, ISO-5752, AWWA C504 (54.0"-72.0")

- Marking: MSS-SP-25

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Classification by connection type

There are different types of concentric butterfly valves depending on the type of connection.

● Wafer type end.

● Lug type end.

● Two flange ends.

● Butt-weld type end.

Butt-clamp type: The butt-clamp type of butterfly valve is designed to maintain a tight seal and prevent differential pressure in both directions to prevent any backflow in equipment built for one-way flow. This is accomplished through the use of precision-machined, tight-fitting covers (e.g., O-rings, gaskets) and smooth valve faces on the downstream and upstream portions of the valve.

 

How does a concentric butterfly valve work?

Concentric butterfly valves are relatively simple in design. The valve body, seals, flaps, and stem are the main components of a concentric butterfly valve. A conventional butterfly valve has a disc located in the middle of the connecting tube and a stem connected to an actuator or handle on the outside of the valve. When the valve is in the closed position, the disc is perpendicular to the fluid and the valve seat is closed. The stem is sealed with an O-ring. When the valve is rotated 90 degrees with the help of the actuator or handle, the disc leaves the seat and is parallel to the fluid. Rotation at an angle of less than 90 degrees allows flow to be throttled or proportional.

 

When to use concentric butterfly valve?

Concentric butterfly valves are made with soft seal materials, so they can only be used for basic (water and wastewater treatment plants), specialty fluids (chemicals, abrasive fluids, etc.), and gases up to 200 psi and 400° F.

● Water treatment.

● Water distribution.

● Water transfer.

● Aeration systems.

● Fire protection, etc.

 

Concentric butterfly valve vs. eccentric butterfly valve

● The structure of concentric butterfly valve disc is simple, while the eccentric butterfly valve disc consists of butterfly plate seal, seal retaining ring, and retaining bolt.

● The sealing structure of concentric valve is very simple, and the valve flap is in direct contact with the rubber seat, while the eccentric butterfly valve uses a laminated seal in contact with the metal seat.

● Concentric butterfly valve is soft seal, and eccentric butterfly valve seat is metal, which can be one-piece seat or replaceable welded seat.

● Concentric butterfly valves have a pressure limit, only up to 150LB/PN25, while eccentric/eccentric butterfly valves can withstand up to 600LB/PN100.

● Due to the difference in sealing structure, concentric rubber seats cannot withstand high temperatures, but eccentric/eccentric butterfly valves have a metal/hard seal design and can work.

● The advantages and disadvantages are obvious, and it is easy to choose which one to use according to the actual situation. Use an eccentric valve when the system has high pressure or high temperature.

An eccentric butterfly valve means that the stem does not pass through the centerline of the valve plate, but is behind it (opposite to the direction of flow). When the stem is directly behind the centerline of the valve plate, the valve is called single offset. This design was developed to reduce the contact between the valve flap and the seal before the valve is fully closed, with the goal of increasing the valve's service life. Today, single eccentric valves have given way to double and triple eccentric butterfly valves. In a double eccentric or double eccentric butterfly valve, the stem is located behind the valve plate and is additionally offset on one side. This double eccentricity of the stem allows the rotating disc to rub only about 1 to 3 degrees on the valve seat.

Triple eccentric butterfly valves are typically used in critical applications and are similar in design to double eccentric butterfly valves. The third offset is the disc seat contact axis. The seat surface is tapered and combines with the same shape of the valve ridge to create minimal contact before the valve is fully closed. Triple eccentric butterfly valves are more efficient and have less wear. Triple eccentric valves are typically made with metal seats to create a gas-tight shutoff. Metal seats allow butterfly valves to be used in higher temperature ranges.

High performance butterfly valve designs use pressure in the pipeline to increase interference between the seat and the edge of the valve plate. These butterfly valves have a higher pressure rating and are easy to wear.

 

Yangzhou Tianshun is a professional butterfly valve manufacturer, if you have any questions, please feel free to contact us.

FAQ:

1. Can I get a sample?

A: Yes, we can provide samples for you

 

2. Can I ask to change the packing and shipping method?

A: Yes, we can change the packing and shipping method according to your request, but you have to bear the cost and price difference in the meantime.

 

3. Can I ask for early delivery?

A: This should depend on whether we have enough stock in our warehouse.

 

4. Can I have my own logo on the product?

A: Yes, you can send us your drawings and we can make your logo, but you must bear the cost yourself.

 

5. Can you produce products according to my own drawings?

A: Yes, we can produce products according to your drawings to your best satisfaction.

 

6. What are your payment terms?

A: T/T, L/C for full protection of your order.

 

7. Do you accept custom design in size?

A: Yes

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