Ptfe-lined Diaphragm Valve Design, Materials And Applications

A lined diaphragm valve uses two fluoropolymer layers. The liner shields the metal body. The diaphragm isolates fluid from the bonnet and actuator. PTFE handles -29°C to 180°C. PFA serves up to 260°C. FEP covers steam to 200°C. The diaphragm and liner must use matched materials.

How to select diaphragm and liner materials?

1. Match the material family (PTFE/PFA/FEP) for both components.

2. Specify diaphragm thickness (3-5 mm) based on pressure class.

3. Verify the liner extends to the flange face for full sealing.

Diaphragm and Liner – A Paired System

The diaphragm seals fluid from the bonnet and closes against the weir. The liner protects the metal body. These components work as a system.

Functional separation:

• Diaphragm: fluid isolation, actuation response, cycle life

• Liner: body protection, flange sealing, weir coverage

A pfa diaphragm valve uses the same fluoropolymer for both components. This prevents seal failure during temperature swings.

Material Selection – PTFE, PFA, or FEP

PTFE (Standard Duty)

A ptfe lined diaphragm valve operates from -29°C to 180°C. The diaphragm uses fabric backing.

    🧪   Hydrochloric acid

    🧪   Sulfuric acid (≤98%)

    🧪   Caustic soda

PFA (High-Temperature)

Continuous service reaches +260°C. A pfa lined diaphragm valve handles hot concentrated acids, oleum, bromine, and high-purity chemicals. The diaphragm can be molded without fabric backing.

FEP (Steam & Hot Water)

FEP suits steam and hot water up to 200°C. Cost-effective where temperature stays ≤150°C continuously.

Selection principle: Diaphragm and liner must use the same material family. Mixing PTFE with PFA causes differential thermal expansion and seal failure.

Diaphragm Design – Thickness and Cycle Life

Thicker diaphragms (4-5 mm) handle higher pressures but need greater actuator force. Thinner diaphragms (2-3 mm) offer faster response but shorter cycle life.

Design parameters:

• Thickness: 3-5 mm based on pressure class

• Stroke: weir height determines travel distance

• Backing: fabric for PTFE, optional for PFA

A teflon lined diaphragm valve uses fabric-backed PTFE for services above PN 10. Diaphragm valves conform to ISO 16138 dimensions.

Liner Design – Weir Coverage and Flange Sealing

The liner covers the weir, body interior, and extends to the flange face. A raised weir provides positive closure with lower force.

Liner requirements:

• Weir coverage: full encapsulation

• Flange extension: 5-10 mm past the flange face

• Corner radius: minimum R 3 mm

• Thickness: minimum 3 mm

The liner must be mechanically locked using dovetail grooves. Without locking, vacuum service pulls the liner from the body.

Actuation and Closure Force

Diaphragm valves need closure force, not torque. The actuator compresses the diaphragm against the weir. Force requirements increase with pressure and bore size.

Actuator types:

• Manual handwheel: self-locking

• Pneumatic: remote on-off and throttling

• Electric: modulating with position feedback

Actuator stroke must match diaphragm travel. Over-travel damages the diaphragm.

Design Checklist with Decision Branches

• Define media, concentration, and temperature.

• Select material:

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

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

  • Saturated steam ≤150°C → FEP.

• Specify diaphragm thickness (3-5 mm).

• Verify liner thickness (minimum 3 mm).

• Confirm mechanical locking features.

• Calculate closure force.

• Select actuator type and stroke.

• Verify flange dimensions.

Chemical Resistance Quick Reference

Sulfuric acid

• ≤98%, ≤120°C → PTFE

• ≤98%, 120–200°C → PFA

• Oleum → PFA only

Chloride and caustic

• HCl, any %, ≤100°C → PTFE

• Wet chlorine → PFA

• NaOH ≤50%, ≤120°C → PTFE

Utilities and solvents

• Saturated steam → FEP (≤150°C)

• High-purity water → PFA

• Organic solvents → PTFE (≤180°C)

Final Selection Summary

Select the material family based on temperature and chemical, then match diaphragm and liner within that family.

• Standard acids and caustics ≤120°C: A ptfe lined diaphragm valve with fabric-backed diaphragm provides reliable service.

• Hot acids, oxidizers, or high-purity: A pfa diaphragm valve is required.

• Steam service: FEP offers a cost-effective option where temperature is ≤150°C.

After selecting the material, verify the mechanical design. Check the P-T rating against maximum operating pressure. Confirm the actuator provides sufficient closure force at maximum differential pressure. Review flange dimensions against piping standards.

If the service involves frequent cycling, consider extending diaphragm thickness or upgrading to PFA for longer cycle life. For critical applications, request prototype testing under simulated process conditions before full-scale installation.

FVF PFA Lined Electric Diaphragm Valve

• FVF lined diaphragm valve adopt special technology by lined PFA/FEP on body, diaphragm is made of PFA/FEP and EPDM,thus all wetted parts are reach same performance of corrosion resistance.
• This valve has good at throttles with advantage of corrosion resistance and abrasion resistance, reliable sealing performance and widely used in corrosive medium, fiber, powder etc. 
• All wetted parts are lined by fluorine, totally isolate from medium to avoid any corrosion on body.