Differences and uses of Off-Set Butterfly Valves

5Ball Valve, Gate Valve or Butterfly Valve?

There are various valve types available to control the flow of fluid and gases, whether to regulate the flow of gases at offshore and onshore infrastructures or isolate a water supply. Ball Valves, Butterfly Valves and Gate Valves have proven to provide effective control and isolation solutions which have been used for many years and serve many diverse industries.

Multi-Purpose and Cost-Effective

Butterfly valves have become universally popular due to their simple, lightweight and compact design, proving a cost-effective solution.

In a concentric butterfly valve, the metal disc can be situated on a shaft which is always centred in the valve body, perpendicular to the flow. When moved to the closed position, the shaft rotates a quarter turn (90 degrees), and the disc turns to completely block fluid flow.

Flow Direction

Concentric butterfly valves can be used for isolating fluids and some throttling applications and are suitable for bi-directional flow.

Disc Closure Design

The discs are usually sealed with the use of a soft elastomeric seat; this elastomeric seat also forms a lining on the inside of the body component allowing materials such as ductile iron to be used in their construction as they do not see contact with the fluid. The lining is typically manufactured from materials such as: EPDM (Ethylene Propylene Diene Monomer rubber) or NBR (Nitrile Butadiene Rubber). The main issue with these simple designs is that the seat is in direct contact with the fluid or gas and therefore can be subject to wear. This may result in a shorter life span of the seat component.

Limitations of the Valve Design

These valves are perfectly suitable for many applications; however, the wear of the seat provides a significantly shorter life for the valve and higher through-life costs when compared to a high-performance equivalent.

High-Performance Butterfly Valves 

As Butterfly Valve designs have evolved, high-performance versions have been developed to reflect changing customer needs and bespoke demanding applications. These valves have several design features which help deliver improved performance, safety, sealing properties and life span. Most high-performance butterfly valves are compatible with off-the-shelf actuation systems.

Body Style Types

Some of the common Butterfly Valve body types include:

• Wafer
• Lugged
• Double-Flanged

High-Performance Butterfly Valve Applications

Improved high-performance valve designs are now being used in more demanding applications. These valves are perfect for use in abrasive or corrosive environments, as well as being used in oil and gas, power generation and energy industries and biotech plants where safety, reliability and high performance are critical considerations.

Double Offset Butterfly Valve

The double-offset butterfly valve’s stem has two offsets from centerlines within the valve.

• The first offset is from the centerline of the seat seal to the centerline of the shaft.
• The second offset is from the centerline of the bore to the centre of the shaft.

The double offset butterfly valve is so-called, because of the previously described offsets. These offsets create a cam action which allows the disc to pull out of the seat within a few degrees of opening from the closed position. The result of this is a significant reduction in friction which the valve experiences throughout the stroke of the valve, resulting in reduced operating torques.

Reducing friction in the valve reduces wear and tear on the disc and seat, and increases the lifespan of the valves, reducing the likelihood of repairs, maintenance, and replacements.

Triple Offset Butterfly Valve

Triple-Offset Butterfly Valves have three offsets, two of which are in the same position as the double-offset butterfly valve, while the third offset is positioned on the seating surface to create a conical-shaped seating geometry.

Advantages of Triple Offset Butterfly Valves

There are some similarities between double-offset butterfly valves and triple-offset butterfly valves. However, the additional design features of the triple-offset range open up additional applications and provide various user benefits, providing an ideal solution for some applications.

The developments in the design provide several advantages that greatly influence the application and the industries that use this valve type.

Benefits

Numerous user benefits are provided by this range, including:

 Performance

• High performance across a diverse range of applications
• Prolonged valve service longevity with the triple-offset design removing seat wear
• Laminated metal seat arrangements provide zero-leakage bi-directional sealing

Design

• Designed fully in accordance with API 609 Category B
• Certified Firesafe design
• Compact design – when compared to other metal seated isolation valves such as Gate Valves
• Peace of mind – multiple Anti-blowout devices integrated into the product to ensure stem retention under all future conditions

Certification and Accreditation

Firesafe certification in accordance with API 607

Actuation

• Standard mounting interfaces enable easy actuation

The main disadvantages of these valves are:

1. Initial upfront cost – can be higher in some situations

Butterfly Valve Applications

The butterfly valve is used across many industries in a wide variety of applications, which include:

• HVAC – for regulating the flow of air in heating, ventilation, and air conditioning systems
• Chemical – for use in regulating the flow of chemicals in chemical manufacturing
• Power generation – for use in controlling the flow of liquids and gases in plant infrastructure
• Wastewater and water treatment – regulate fluid flow in water treatment plants

Conclusion

Butterfly valves are versatile and robust valves used in corrosion-resistant and severe applications, making them the long-term preferred isolation solution for many industries.

The benefits of these valves far outweigh the disadvantages, making them a wise investment for many industries.

However, the benefits of these valves far outweigh the disadvantages, making them a wise investment for many industries. To speak to an expert member of staff today, get in touch with us.