Principle And Selection Of Fluorine-lined Butterfly Valves

A lined butterfly valve combines a metal body for pressure containment with a fluoropolymer liner for corrosion resistance. The liner covers all wetted surfaces, isolating aggressive media from metal. PTFE handles -29°C to 180°C. PFA serves up to 260°C. FEP covers steam and hot water to 200°C.

Which liner material suits your corrosive media?

1. Standard acids and caustics ≤120°C → PTFE.

2. Hot acids, oxidizers, or high-purity → PFA.

3. Steam and hot water ≤150°C → FEP.

Dual Protection Principle

The metal body handles pressure. The liner handles corrosion. Neither performs both functions.

Structural components:

• Body: ductile iron or cast steel, PN 10 to PN 40

• Liner: PTFE, PFA, or FEP

• Disc: fully encapsulated with fluoropolymer

• Stem: stainless steel with fluoropolymer sleeve

• Seat: integrally molded with liner

A ptfe lined butterfly valve handles hydrochloric acid, sulfuric acid (≤98%), and caustic soda. Wafer and lug designs conform to ISO 5752 and API 609 face-to-face dimensions.

Lining Material Selection

PTFE (Standard Duty)

• -29°C to 180°C, PN 10-25

• Services: hydrochloric acid, ≤98% sulfuric acid, caustic soda, chlorine gas

PFA (High-Temperature / Oxidizer Duty)

• Up to 260°C, lower permeability, pinhole-free injection-molded lining

• Services: hot concentrated acids, oleum, bromine, high-purity chemicals

FEP (Steam & Hot Water)

• Up to 200°C (≤150°C continuous), cost-effective

Selection principle: PTFE and PFA resist the same chemicals. PFA offers lower permeation and higher temperature tolerance.

Seat and Disc Design

The seat integrally molds with the liner, creating a continuous seal. This eliminates separate seat rings that could shift or leak. The disc is fully encapsulated, ensuring no metal contacts the media.

A teflon lined butterfly valve uses this design for bubble-tight shut-off.

Seal integrity factors:

• Disc-to-seat interference: engineered per pressure class

• Stem sealing: O-rings or fluoropolymer packing

• Face-to-face dimensions: ISO 5752 or API 609

Actuation and Torque

Operating torque varies with liner material and temperature. PTFE requires lower torque than PFA at the same temperature. Torque increases with temperature for all fluoropolymers.

Actuator options:

• Lever: DN 150 max, low pressure

• Worm gear: DN 200+, self-locking

• Pneumatic: remote on-off, emergency shutdown

• Electric: modulating control

Oversize actuators for pfa lined butterfly valves due to higher friction.

Selection Checklist with Decision Branches

1. Verify piping class and flange standard.

2. Confirm media, concentration, and temperature.

3. Select liner:

   • Standard acid/caustic ≤120°C → PTFE.

   • Sulfuric acid >98% or hot acid >120°C → PFA.

   • Saturated steam ≤150°C → FEP.

4. Choose body material based on pressure.

5. Specify disc type (wafer or lug).

6. Verify P-T rating curve.

7. Confirm dimensions per API 609.

8. Select actuator type and torque.

Chemical Resistance Quick Reference

Sulfuric acid

• ≤98%, ≤120°C → PTFE

• ≤98%, 120–200°C → PFA

• Oleum → PFA only

Chloride & caustic

• HCl, any %, ≤100°C → PTFE

• Wet chlorine → PFA

• NaOH ≤50%, ≤120°C → PTFE

Utilities & solvents

• Saturated steam → FEP (≤150°C)

• High-purity water → PFA

• Organic solvents → PTFE (≤180°C)

Select the liner based on your process conditions, then verify the valve meets the mechanical requirements of the system.

Liner decision:

• Standard acids and caustics ≤120°C → PTFE provides reliable, cost-effective service.

• Hot acids, oxidizers, or high-purity processes → PFA is required.

• Steam service ≤150°C → FEP offers a cost-effective alternative.

Mechanical verification: After selecting the liner, confirm the body material, pressure rating, and end connections match the piping specification. Check the pressure-temperature curve against the maximum surge pressure in the system. 

FVF Lug Type PTFE Lined Butterfly Valve With Worm Gear

• FVF lined butterfly valve can realize  bi-directional flow under the maximum working pressure.Since the valve port corresponds to the piping diameter, a high flow capacity is guaranteed.
• It features ease of maintenance, repeatable on-off, long life durability.
• It is commonly used in the power generation, brewing, water and food industries and suitable for both gaseous and liquid service. Typically applied in chemical/petrochemical process, food and beverage, and pulp and paper etc.
• They are available with Wafer style or Lug style 150# ANSI flange connections. They can be equipped with a manual lever or can be actuated with electric or pneumatic actuators. A full range of accessory items are available including limit switches, solenoid valves, positioners and manual override devices.