Butterfly Valves

What is a Butterfly Valve?

Butterfly valves are typically used in isolation or moderate flow control applications. The obturator is a disc that is always present in the bore of the valve and is mounted on a shaft which turns 90 degrees to open or close the valve.

This type of valve is suitable for many industries, including shipbuilding, chemical processing, petrochemicals, oil and gas, power generation, and pharmaceuticals. These quarter-turn valves are the preferred choice and a suitable alternative for gate and ball valves in many industries due to their ease of operation, compact design, low maintenance and throttling functions.

How do butterfly valves operate?

Essentially, manual butterfly valves are operated by levers or handwheels attached to a gearbox that drives the shaft. When the disc is perpendicular to the bore of the valve it is in the closed position. When closed the valve stops the flow of media (either gas or liquid). It is possible to use a butterfly valve to throttle moderate pressure drops, this can be achieved by partially opening the valve. When throttling a fluid it is advisable to do this at low to moderate openings of the valve. When fully open the disc is still in the flow path, however, this creates minimal restriction to flow. Where required butterfly valves may be operated using actuators either pneumatic, electric or hydraulic actuators could be applied to these valves.

Advantages of butterfly valves over other valve types

The butterfly valve in its simplest form has been in existence since the 1900s and is one of the most widely used valves today, providing several advantages over other valve types such as:

• Its simple design means it is relatively easy to maintain
• Are well suited for large-diameter pipeline applications due to their lower weight and cost when compared to other valve types
• They can be installed horizontally or vertically in pipelines
• The metal-seated butterfly valves aim to deliver zero seat leakage making them a perfect isolation solution for high-temperature or slurry applications
• Speed of operation, when actuated cycle time compared to a linear valve is much shorter
• Compact design allows for installation in confined spaces
• Options available to support various applications, including those with high temperatures

Disadvantages of butterfly valves

• The location of the shaft across the bore does not allow for pipes to be ‘pigged’. Where pigging is to be carried out butterfly valves shall not be used
• They are not recommended for areas where there is a potential for process medium ‘slugging’ or where bulk solids or fibrous materials in the pipeline may cause clogging and damage to the valve

Concentric Butterfly Valves

Butterfly Valves were first designed as concentric valves, where the shaft and disc are aligned with the centre of the bore. With this design of valve when the disc in the valve pulls through a non-metallic, typically elastomeric liner which also acts as the seat or seal for the valve. The continuous compression working of the liner of the valve makes this valve design suited to low-pressure and non-critical applications.

Single-Offset Valves

In a single-offset valve, the shaft is not centrally located back from the seat or seal in the valve. This butterfly valve design is ideal for applications that have space constraints or a smaller valve is required.

Double-Offset Butterfly Valves

A Double-Offset Butterfly Valve is designed where the shaft is offset in two directions from the centrelines of the pipe and seat. By using a double-offset design a PTFE seat and a fire-safe (metallic) seat may be used to achieve zero-leakage and a fire-safe design.

Triple-Offset Butterfly Valves

The Triple-Offset Butterfly Valve uses an additional offset when compared to the Double-Offset Butterfly Valve. This additional offset puts an angle on the seat making it a conical profile, the conical seat allows for the use of metallic sealing faces on both the disc and the seat. The Triple-Offset design uses a torque seated design allowing the valve to open and close with contact occurring on the seating faces only when the valve is closed.

Wafer-Type

A Wafer-Type Butterfly Valve is commonly used in low-pressure applications where it is clamped between the two pipeline flanges. Its compact size makes it an attractive option when compared to other types. This type is recommended for use in general-purpose, non-critical applications.

Lug-Type

Lug-Type Butterfly Valves have lugs which are cast integral to the valve body. When installing this type of valve the flange bolting goes through drilled or threaded holes in the lugs which align the valve to the pipe. The valve is then clamped between the two flanges just like the wafer-type valve. This valve type gives a much better seal between the valve and the mating flanges than a wafer-type version.

This valve type is recommended for use in general-purpose applications and may be used for a dead-end service when threaded lugs are furnished on the valve.

Double-Flanged

Double-Flanged Butterfly Valves have two flanges, one at either end of the body, which is used to bolt the valve to the pipeline flanges. This valve is used in critical applications, where the integrity of the pipeline is critical but not critical enough to make use of welded ends.

Lever

The most common type of manual actuator is the lever. The lever is attached to the shaft of the butterfly valve and used to turn it. This simple mechanism allows the valve to be locked open or closed. These are typically used on smaller valves where the operating torques require no mechanical advantage to operate the valve.

Gearbox

A gear operator is a type of mechanical actuator used to operate a butterfly valve. A handwheel is used to turn the valve open via a gear system. The operation of the valve is slower than compared to a lever, however, the mechanical advantage offered by the gearbox enables the valve to be operated manually rather than with actuation.

Actuation

Actuation is used when the butterfly valve needs to be operated frequently, where the operating load exceeds manual operation or remote operation is needed. The actuators may use hydraulic, pneumatic or electric power to turn the shaft and operate the butterfly valve.

Pneumatic

Pneumatic actuators are powered by compressed air. Pneumatic actuators are available in single-acting (spring return) or double-acting (air to open, air to close).

Electrical

Electric actuators are powered by an electric motor and are used in applications where there is a need for remote operation.

Hydraulic

Hydraulic actuators use hydraulic fluid to power the movement of the butterfly valve. Hydraulic actuators are also available in single-acting (spring return) or double acting (hydraulic to open, hydraulic to close).

Bubble tight shut-off

The bubble-tight shut-off is essential for various applications to prevent leakages, environmental contamination or product loss. High-performance butterfly valves are designed and manufactured to deliver excellent sealing performance.

Zero Leakage is critical for many applications to prevent environmental contamination, and product loss or to ensure the product is fit-for-purpose. High-performance butterfly valves are designed and manufactured to provide superior sealing performance.

Butterfly valves are used in a wide variety of industries for the isolation and control of fluid flow. They are suitable for use with a wide range of fluids including air, water, steam, oil, and gas. They are also suitable for use with aggressive fluids such as acids and alkalis.

Butterfly valves are used in a wide variety of industries and applications including:

• Chemical and process plants
• Heating, ventilation and air-conditioning (HVAC) systems
• Marine applications
• Oil and gas production
• Paper mills
• Pharmaceutical manufacturing
• Pipeline infrastructure
• Power plants
• Water treatment plants

Shipham Valves have supported the complex valve needs of the pipeline industries and infrastructure for over 90 years. From a standard valve range to bespoke and high-performance butterfly valves.