Butterfly Valve Types: A simple (But Complete) Guide

By Material

Cast iron butterfly valves are the most common type, suitable for low-pressure and normal temperature water systems, with good strength and wear resistance, but not ideal for corrosive environments.

Cast steel butterfly valves are suitable for medium and high-pressure applications, such as in the oil, natural gas, and chemical industries. They offer better strength and high-temperature resistance; however, users should exercise caution when using them in extremely corrosive media.

Stainless steel butterfly valves are widely used in the food, pharmaceutical, and other industries due to their excellent corrosion resistance and hygienic performance. They can withstand higher temperatures and pressures, and their maintenance is relatively simple, although they come at a higher cost.

Plastic butterfly valves (such as PP or polyvinyl chloride) are lightweight and corrosion-resistant, suitable for chemical transport and sewage treatment, but with lower strength and temperature resistance.

Users often employ special materials such as duplex steel and nickel alloy butterfly valves in extreme environments because they provide better corrosion resistance and mechanical strength, although they come at a higher cost.

Concentric Butterfly Valve

A center-sealed butterfly valve is a common structural form of butterfly valve, and its design feature is that the rotational center of the butterfly plate coincides with the center of the valve stem, which is located on the center line of the valve body. When the valve is closed, a certain amount of interference is generated between the butterfly plate and the valve seat, thus generating a sealing force to ensure the sealing of the valve.

This design causes the upper and lower valve stems to be subjected to severe compressive stress, which affects the service life of the valve, and the switching torque is also relatively high.

However, the structure of the center-sealed butterfly valve is relatively simple, consisting of a few parts, small in size, light in weight, simple in operation, requiring only a 90° rotation to open and close quickly, with good flow control characteristics and low-pressure loss. To overcome the problem of extrusion and scratching, center-sealed butterfly valves usually use elastic materials such as rubber or PTFE as sealing rings, but temperature is still a limiting factor, which is why conventional butterfly valves are usually not resistant to high temperatures.

Single Offset Butterfly Valve

Its main feature is that the rotating center of the butterfly plate forms a certain eccentric distance from the center line of the valve body. This design makes the butterfly plate gradually separate from the valve seat during the opening process, effectively reducing the extrusion and wear during switching and improving the valve seat's service life. 

Compared with the center-sealed butterfly valve, the single eccentric butterfly valve performs better in reducing wear and tear. However, there is still a certain amount of scraping phenomenon, which limits its application range.

Single offset Butterfly Valves are suitable for low and medium-pressure environments and perform well, especially in the chemical and water treatment fields. However, as double and triple eccentric butterfly valves offer superior sealing performance and durability, the latter is often preferred for demanding applications.

Double Offset Butterfly Valve

The deviation of the centre of rotation of the valve plate from the centre line of the valve seat significantly improves sealing performance. This design results in a significant reduction in opening torque, especially in large bore and high pressure conditions, and is therefore widely used in the oil and gas industry.

Double eccentric butterfly valves perform well in handling fluids containing solid particles and have a significantly longer service life than other types, and the reduced stress on the sealing element results in reduced maintenance requirements, making them suitable for long-term stable operation.

Triple Offset Butterfly Valve

Triple Eccentric Seal Butterfly Valves have three unique eccentric features related to stem position, butterfly plate-to-seat sealing surface deviation, and the conical geometry of the sealing surface.

The metal-to-metal sealing mechanism of the Triple Eccentric Butterfly Valve eliminates friction, reduces wear, and lowers operating torque, making it ideally suited for automated control.

The Triple offset Valve excels when handling corrosive media and high temperature steam, preventing leakage and reducing maintenance requirements. In addition, its cavity-less design prevents the accumulate of contaminants, further reducing maintenance costs.

Source: Instrumentation Tools

Wafer Butterfly Valve

They are suitable for use in areas such as water treatment, HVAC systems and low pressure gas distribution. They are simple in design and relatively easy to install and maintain. However, Butterfly Butterfly Valves cannot be used as isolation valves.

As sealing performance may be limited under high pressure conditions, it is necessary to ensure that the sealing material (e.g. EPDM or NBR) is suitable for the fluid medium when selecting to prevent leakage.

Lug Butterfly Valve

Lug type butterfly valves are named for their protruding ears, these lugs are located on the outer edge of the valve body, allowing the valve to be mounted between two flanges by bolts passing through the lugs and flanges to form a strong connection. Lug butterfly valves are mostly of triple eccentric design, which can provide bi-directional and bubble-free sealing performance. It has better isolation capability compared to the Wafer type.

And they can be disassembled on one side without affecting the connection on the other side, which is very suitable for systems requiring frequent maintenance, such as fire-fighting water systems and certain chemical processes. However, they are generally suitable for low to medium pressure environments and may not be strong enough for high pressures.

Selecting lug type butterfly valves made of stainless steel or alloy materials can improve corrosion resistance and strength. Also, make sure that the bolts selected match the valve material to avoid failures due to corrosion between different materials.

Flanged Butterfly Valves

Flanged butterfly valves are larger and have flanges on the valve body, which are usually bolted to the flange of the pipeline.

Flanged butterfly valves are widely used in high-pressure or high-temperature environments such as petroleum, natural gas, chemical industry, and paper-making. The flanged connection provides better support and is suitable for long time operation. They can also be used for dead-end service, and promote system maintenance and overhaul.

When selecting, you need to ensure that the flange standard (e.g. ANSI, DIN, JIS, etc.) matches the pipe to avoid installation problems. A double seal design can be considered to simultaneously improve sealing performance and extend service life.

Welded Butterfly Valve

Welded butterfly valves are welded directly to pipework to provide extreme strength and sealing. They are commonly used in critical service environments where tight sealing is required, such as oil, gas and chemical transport. They offer high pressure and temperature resistance, making them suitable for use in harsh working conditions. This type of lined valve is uncommon because most plastic-lined valves have flange size limitations (PN10/16 (150#)).

Welded connections reduce the risk of leakage, but they are difficult to remove and repair once installed. So consider using removable welded connections that can also be maintained when needed.

Source：Global Valve Center

The main differences between high-performance butterfly valves and ordinary butterfly valves are material, design, sealing performance and application scenarios.

High-performance butterfly valves usually adopt double- or triple-eccentric design, which enables the valve flap to better separate from the valve seat when opening, thus reducing wear and improving the sealing effect. This design makes use of pipeline pressure to enhance sealing performance, while ordinary butterfly valves are mostly center-sealed or single eccentric structures, with relatively poor sealing performance and limited scope of application.

The sealing ring of high-performance butterfly valves is usually made of a combination of soft materials and metal sheets, which can achieve zero-leakage sealing in low and high-temperature environments, while the sealing ring of ordinary butterfly valves is mostly made of a single material, which may not be able to meet the strict sealing requirements.

High-performance butterfly valves perform well in petroleum, chemical and electric power, metallurgy and other industries, while ordinary butterfly valves are more suitable for low-pressure water systems, HVAC, fire-fighting and other applications that do not require strict sealing.