Butterfly Valve Body
The valve body is positioned between the pipe flanges and houses the internal components of the valve. It is typically made from metal, with materials including carbon steel, stainless steel, titanium alloy, nickel alloy, or aluminum bronze. All materials except carbon steel are suitable for corrosive environments.
The body of a butterfly valve comes in three main types:
Lug Type
- Features protruding lugs with bolt holes that align with those in the pipe flange.
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Allows for dead-end service or removal of downstream piping.
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Threaded bolts around the entire body make it a safer option.
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Suitable for end-of-line service.
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Weaker threads result in lower torque ratings.

Wafer Type
- Lacks protruding lugs and is sandwiched between pipe flanges using flange bolts.
- Includes two or more centering holes to assist with installation.
- Does not transfer the weight of the piping system directly through the valve body.
- Lighter and more cost-effective than lug-type designs.
- Cannot be used at the end of a pipe.

Double Flanged Type
- Features complete flanges on both ends to connect with pipe flanges.
- Commonly used for large-size valves.

Butterfly Valve Disc
- The disc acts as the gate to start, stop, or regulate fluid flow. It is analogous to the ball in a ball valve. Discs are typically made from metals such as ductile iron, aluminum, or stainless steel but can also be coated with materials like nylon or nickel for enhanced performance.
- The disc rotates 90 degrees (a quarter-turn) to open or close the valve. When designed precisely, the disc aligns perfectly with the valve seat to create a tight, leak-proof seal.

Butterfly Valve Stem
- The stem connects the disc to the actuator and controls its movement. The type of stem required depends on whether it will come into contact with the fluid media:
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In resilient-seated designs, the stem is typically protected and does not contact the fluid.
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In high-performance valves, the stem often comes into contact with the fluid.
- Stems can be either a one-piece shaft or a two-piece (split-stem) design. The stem is mounted on a vertical axis at the center of the disc and is connected to the actuator. A seal along the edge of the disc’s elastomer lining ensures a tight shut-off.
- For high-performance butterfly valves, the shutoff mechanism may involve:
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Interference-fit seat design: The seat and disc edge are designed to fit tightly together.
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Line-energized seat design: Pipeline pressure increases the interference between the seat and disc edge for a stronger seal.

Butterfly Valve Seat
- The seat is a critical component that ensures a leak-proof seal when the valve is closed. In rubber-seated valves, the seat is made from elastomers or polymers, creating a “soft” seal. This design is ideal for low-torque applications.
- Common seat materials include:
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Teflon (PTFE): Versatile, heat-resistant, and durable.
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EPDM: Suitable for water and steam applications.
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White EPDM: Often used in food-grade applications.
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Buna N: Resistant to oils and fuels.
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Viton: Ideal for high-temperature and chemical-resistant applications.
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Silicone: Used in high-temperature and food-grade applications.
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Neoprene: Resistant to abrasion and weathering.
- Food-grade seating materials, are specifically designed for applications requiring compliance with food safety standards.

In summary, the butterfly valve consists of several key components—body, disc, stem, and seat—each playing a vital role in its operation. The choice of materials and designs depends on the specific application, ensuring optimal performance, durability, and reliability.