What are the different types of Butterfly Valves?

Butterfly valves are generally divided into three primary designs:

• Concentric (Resilient-Seated) — A centered disc that seals against an elastomer seat. Best suited for low- to moderate-pressure services such as water, HVAC, and general utility applications.
• Double Offset (High-Performance) — Two shaft offsets reduce friction between the disc and seat, improving sealing performance, cycle life, and suitability for higher pressures and temperatures.
• Triple Offset (Metal-Seated) — A three-offset geometry with a metal-to-metal conical seal that eliminates rubbing during operation, making it ideal for severe service, including high-temperature steam, hydrocarbons, and other critical process applications.

The primary difference between these designs is how the disc engages the seat, which directly affects sealing performance, operating torque, service life, and the environments in which the valve can be used.

Why It Matters

Choosing the right butterfly valve is about far more than simply selecting a pressure class. The valve design determines how well it seals, how long it will last, how much torque is required to operate it, and whether it can withstand the process conditions over its service life.

Using a resilient-seated butterfly valve in a high-temperature steam application, for example, can quickly damage the elastomer seat and lead to leakage or premature failure. Conversely, specifying a triple offset valve for a basic cooling water system may provide little practical benefit while significantly increasing equipment and actuation costs.

Selecting the appropriate valve type helps improve:

• System reliability
• Service life and maintenance intervals
• Shutoff performance
• Operating torque and actuator sizing
• Compliance with applicable industry standards

Understanding the Three Butterfly Valve Designs

Concentric Butterfly Valves

Concentric butterfly valves—often called resilient-seated butterfly valves—feature a disc and shaft positioned directly in the center of the valve body. The disc seals against an elastomer seat, commonly manufactured from materials such as EPDM, NBR, or PTFE.

Because the disc remains in contact with the seat throughout most of its travel, this design produces excellent bubble-tight shutoff but also creates friction during every operating cycle. Over time, repeated rubbing can increase seat wear, particularly in throttling or high-cycle applications.

Advantages

• Simple, economical construction
• Bubble-tight shutoff for many utility services
• Low maintenance in clean, low-pressure applications

Limitations

• Continuous seat contact increases wear
• Limited by elastomer temperature and chemical resistance
• Less suitable for demanding pressure or throttling applications

Typical applications include water treatment, HVAC systems, irrigation, cooling water, and other general utility services.

Double Offset Butterfly Valves

Double offset, or high-performance butterfly valves, relocate the shaft in two directions:

• Offset from the pipe centerline
• Offset from the plane of the sealing surface

These offsets allow the disc to disengage from the seat almost immediately after opening begins, dramatically reducing rubbing between the sealing surfaces.

The result is lower operating torque, longer seat life, and improved performance in higher-pressure and higher-temperature applications. Seats are commonly manufactured from reinforced PTFE or other engineered polymers that provide greater chemical and thermal resistance than traditional elastomers.

Advantages

• Reduced seat wear
• Longer service life
• Lower operating torque
• Better performance under elevated pressure and temperature

These valves are widely used in chemical processing, power generation, industrial utilities, and many oil and gas applications where resilient-seated valves have reached their practical limits.

Triple Offset Butterfly Valves

Triple offset butterfly valves incorporate a third geometric offset that creates a conical sealing surface. Instead of sliding across the seat during operation, the disc follows a cam-like motion and contacts the seat only at the final moments of closure.

This non-rubbing action greatly reduces sealing surface wear and allows the valve to use durable metal seating rather than elastomeric materials. Hard-facing alloys such as Stellite are commonly applied to improve wear and erosion resistance.

Advantages

• Virtually eliminates rubbing between sealing surfaces
• Excellent performance in high-temperature and high-pressure service
• Long service life
• Suitable for severe process applications
• Fire-safe designs are available

Depending on the valve design and applicable leakage standard, triple offset valves can achieve extremely low leakage rates while maintaining reliable performance in demanding operating environments.

Their primary disadvantages are higher purchase cost and tighter installation tolerances, both of which are typically justified in critical service.

Typical Applications

Concentric

• Water and wastewater treatment
• HVAC systems
• Cooling water
• General utility service

Double Offset

• Chemical processing
• Power generation
• Industrial process systems
• Oil and gas facilities

Triple Offset

• Steam systems
• Petrochemical plants
• Refineries
• High-pressure gas service
• Severe process applications

Actual service limits always depend on valve materials, pressure class, seat design, and manufacturer ratings.

How to Select the Right Butterfly Valve

Selecting the appropriate butterfly valve begins with understanding the application rather than simply choosing a valve style.

Key considerations include:

• Operating pressure and temperature
• Process media compatibility
• Required shutoff performance
• Frequency of operation
• Expected service life and maintenance requirements
• Applicable industry standards and customer specifications

As operating conditions become more demanding, the preferred valve design generally progresses from concentric to double offset to triple offset.

Materials and Actuation

Butterfly valves are manufactured in materials ranging from ductile iron for municipal water service to carbon steel and stainless steel for more demanding industrial applications.

Seat selection is equally important. Elastomeric seats provide economical sealing for general service, engineered polymer seats extend temperature and chemical capability, and metal seats allow operation in environments where soft materials would rapidly fail.

Common actuation methods include:

• Manual lever or gear operators
• Pneumatic actuators
• Electric actuators
• Hydraulic actuators

When sizing an actuator, the required valve torque—including pressure effects, seating torque, and safety factors—should always be considered.

Common Selection Mistakes

Some of the most common butterfly valve selection errors include:

• Assuming every butterfly valve provides the same shutoff performance
• Selecting seat materials without confirming chemical compatibility
• Treating double offset and triple offset valves as interchangeable
• Ignoring installation alignment requirements
• Underestimating actuator torque requirements

Most premature butterfly valve failures can ultimately be traced back to improper application rather than defects in the valve itself.

Installation and Maintenance

Proper installation plays a major role in butterfly valve performance and service life.

During installation:

• Verify flange alignment before tightening bolts.
• Ensure adequate disc clearance before cycling the valve.
• Tighten flange bolts according to the manufacturer's recommended sequence and torque values.

Routine maintenance should include periodic inspection of the seat, disc, shaft seals, and actuator, along with monitoring for leakage or increasing operating torque that may indicate developing wear.