Main Butterfly Valve Parts and How They Work

Valve Body

The valve body is the main structural component of a butterfly valve. It connects to the pipeline and houses internal parts such as the disc, stem, and seat. In addition to withstanding pipeline pressure, the valve body also determines the installation method and suitable working conditions of the butterfly valve.

Based on the connection design, butterfly valve bodies are generally divided into three types:

• Wafer Type: Installed between two pipe flanges and secured by bolts passing through the flanges. This design is compact and lightweight.
• Lug Type: The body is designed with threaded lugs, allowing flange bolts to be directly fastened into the valve body. This makes it possible to remove one side of the pipeline independently for easier maintenance.
• Flanged Type: Both ends of the valve body have full flanges and are connected to the pipeline flanges with bolts. This structure provides a stronger connection and is commonly used for larger sizes and higher-pressure applications.

Common valve body materials include cast iron, ductile iron, carbon steel, and stainless steel.

Valve Disc

The valve disc is the core opening and closing component inside a butterfly valve. It is usually disc-shaped, positioned at the center of the pipeline, and connected to the actuator through the valve stem.

When the stem rotates, the disc rotates together with it:

• When the disc is parallel to the flow direction, the valve is fully open.
• When the disc is perpendicular to the flow direction, the valve is fully closed.

The disc typically rotates 90 degrees (a quarter turn) to move the valve from fully open to fully closed.

In addition to fully open and fully closed operation, the disc can also remain at intermediate angles to provide flow control and throttling functions.

Common disc materials include:

• Ductile Iron
• CF8
• CF8M
• Aluminum Bronze
• Duplex Stainless Steel

Among these materials, stainless steel and aluminum bronze discs are widely used in water treatment, seawater, and industrial media systems because of their excellent corrosion resistance.

Valve Stem

The valve stem is the key transmission component that connects the butterfly valve actuator — such as a lever handle, gearbox, electric actuator, or pneumatic actuator — to the valve disc. Its main function is to transfer operating torque from the actuator to the disc, allowing the valve to open and close.

Depending on the design structure, butterfly valve stems are generally divided into the following two types:

• Single Stem: A single stem passes through the valve body and disc, usually connected by pins or a square drive design. This structure is simple, strong, and commonly used in small to medium-sized butterfly valves.
• Double Shaft: The stem is divided into upper and lower shafts that connect separately to the disc. This design helps reduce flow resistance and valve weight, making it more suitable for large-diameter butterfly valves.

Valve Seat

The valve seat is the key sealing component inside a butterfly valve. It is usually installed on the inner wall of the valve body or around the edge of the disc. When the disc closes, its outer edge presses tightly against the seat to shut off the flow of media.

Based on different structural designs, butterfly valve seats are generally divided into the following types:

• Bonded Seat: The seat is permanently bonded to the valve body as one piece. This design is simple and cost-effective, and is commonly used in concentric butterfly valves.
• Replaceable Seat: The seat can be removed and replaced separately, making maintenance easier and helping extend the overall service life of the valve.
• Metal Seat: Uses a metal-to-metal sealing design and is suitable for high-temperature, high-pressure, and abrasive media applications. It is commonly used in double offset and triple offset butterfly valves.

The seat material directly affects the sealing performance, temperature resistance, and service life of a butterfly valve.

Common seat materials include:

• EPDM: Commonly used in water treatment, HVAC, and chilled water systems
• NBR: Suitable for oil and certain gas applications
• PTFE: Widely used for corrosive chemical media
• Metal Seat: Designed for high-temperature, high-pressure, and abrasive service conditions

In soft-seated butterfly valves, the seat is usually the component most prone to wear and aging, making it one of the most commonly replaced parts.

Bearing

Bearings are installed between the valve body and the stem. Their main function is to support the stem and reduce friction during rotation. Bearings help keep the stem properly aligned, improve the smoothness of valve operation, and reduce operating torque.

Depending on the valve design, one or more bearings may be installed at the upper and lower stem positions inside the valve body. In large-diameter butterfly valves and double offset butterfly valves, bearings are especially important for operating performance and service life.

Common bearing materials include:

• Bronze
• PTFE Bushings
• Stainless Steel Bearings
• Self-Lubricating Bearings

Actuator

The actuator provides the operating force required to open and close the butterfly valve. Depending on the level of automation and application requirements, butterfly valves can be equipped with different types of actuators.

Common actuator types include:

• Lever Handle
• Worm Gear Operator
• Pneumatic Actuator
• Electric Actuator

Small-diameter butterfly valves are commonly operated by lever handles, while larger butterfly valves are more often equipped with worm gear operators, electric actuators, or pneumatic actuators to reduce operating torque and enable automated control.

Butterfly Valve Assembly

 Although the structure of a butterfly valve may appear relatively simple, each component plays an essential role in valve operation. Understanding the structure and function of each butterfly valve part not only helps with proper valve selection, but also makes maintenance and troubleshooting easier.

As a professional industrial valve manufacturer, Union Valve provides a wide range of butterfly valve solutions, including concentric butterfly valves, double offset butterfly valves, and triple offset butterfly valves for water treatment, HVAC, municipal water supply, and industrial piping applications. If you would like more information about butterfly valve products or technical support, feel free to contact Union Valve at any time.

FAQ

What are the main parts of a butterfly valve?

A butterfly valve mainly consists of the valve body, disc, stem, seat, bearings (or bushings), and actuator. These components work together to control opening, closing, and flow regulation.

Which butterfly valve part wears out most easily?

In soft-seated butterfly valves, the seat is usually the component most prone to wear and aging. Frequent operation, media erosion, and temperature changes can all affect sealing performance, which is why the seat is one of the most commonly replaced parts.

Can the valve seat of a butterfly valve be replaced separately?

This depends on the seat design. A replaceable seat can be removed and replaced separately, while a bonded seat is usually fixed to the valve body and cannot be replaced independently. Repair or replacement methods will vary depending on the specific valve design.

Related Articles:

• Butterfly Valve Seat Types, Materials, and Selection Guide
• How to Choose the Right Butterfly Valve Type
• How to read butterfly valve specifications for your needs
• How Does a Butterfly Valve Work