Key Design Considerations And Performance Of Fluorine-lined Check Valves

Spring corrosion causes check valve backflow. Lined check valves require three design pillars: body material (ductile iron or steel for pressure containment), liner material (PTFE, PFA, or FEP for corrosion barrier), and spring encapsulation (PFA/PTFE coating to prevent media contact). Specify PTFE for service up to 180°C. Select PFA above 180°C. Springs fail first due to fretting wear under cyclic loading – full encapsulation is the primary design.

Why Standard Check Valves Fail

Metal check valves exposed to acids, alkalis, or chlorides fail via:

• Spring corrosion → loss of closing force

• Pitting/crevice attack at seat and disc

• Stress corrosion cracking of springs

• Galvanic corrosion between dissimilar metals

Consequences: Backflow, leakage, unplanned downtime, and upstream contamination.

Construction – Three Design Pillars

The body contains pressure, the liner resists corrosion, and the spring/disc are fully isolated from media – double isolation ensures reliability.

Body Material Selection

• Ductile iron: Standard up to PN 25, cost-effective.

• Cast steel (WCB/LCB): For PN 40+ or low-temperature service.

• Stainless steel (CF8M/CF3M): For external corrosion (marine/aggressive atmospheres).

Rule: Body withstands pressure and thermal stress – corrosion resistance is the liner’s job.

Liner Material – PTFE, PFA, and FEP

• PTFE lined check valve: For most acids/bases/solvents, max 180°C.

• PFA lined check valve: Higher strength and thermal stability, max 260°C, lower permeability.

• Teflon lined check valve (generic term): Covers both PTFE and PFA. Distinguish by color (PTFE white/off-white, PFA translucent/light gray) and temperature label.

Selection: PTFE for <180°C, PFA for >180°C, FEP for steam/hot water with cost constraints.

Spring Encapsulation – Design Focus

Why springs fail first: Springs undergo cyclic loading (compression/release each cycle), causing fretting wear on encapsulation. Micro-cracks or pinholes allow media penetration, leading to spring corrosion, loss of elasticity, and valve failure.

Encapsulation requirements:

• Full molding in PFA or PTFE, 2–3 mm thickness

• Spark testing to detect pinholes

• Chemical roughening for adhesion

Verify: Spring closing force at maximum operating temperature – PFA/PTFE softens at high temp.

Disc Type Selection – Ball, Piston, Swing

PTFE lined ball check valve: Spherical disc, low ΔP, self-centering – for low flow.
Piston: Cylindrical, positive sealing – for higher velocities.
Swing: Hinged, minimal resistance – for large diameters.

Cracking Pressure and Pressure Drop

• Cracking pressure: Upstream pressure to open – depends on spring force and disc weight.

• Pressure drop: Loss when fully open – affected by flow, disc design, liner finish.

Performance notes: PTFE is smoother but less wear-resistant; PFA offers smoother finish and lower ΔP. Higher spring force raises cracking pressure but improves sealing.

Installation and Maintenance Basics

• Install with flow arrow; straight pipe runs upstream 5D, downstream 3D.

• Support heavy piping; torque flange bolts to prevent liner cracking.

• Inspect liner for scratches; check disc/seat wear; re-torque after thermal cycles.

• Avoid vertical installation without orientation check; never exceed temperature rating.

Troubleshooting – Diagnosis, Cause, Solution

How to Specify

Define media, temperature, pressure, and flow. Select liner (PTFE/PFA/FEP), body material, disc type, and cracking pressure. 

Lined check valves rely on body strength, liner resistance, and spring encapsulation. PTFE lined for ≤180°C, PFA lined for ≤260°C; Teflon lined is generic – verify grade. Spring encapsulation determines reliability – without complete coating, springs corrode and fail. Select based on media, temperature, pressure, and flow.

FVF PTFE PFA FEP Lined Lift Through-Way Check Valve

• FVF lined check valve only allow one way flow direction and prevent the back-flow of liquids in pipeline. Generally check valve is automatically working.Under the pressure function of one direction flow, the disc open, while when the liquid back flows, the valve will cut flow.When it is used as vertical installation, it will not set the spring. Using the disc weight and backflow pressure to achieve the check effect.
• FVF lined check valve is mainly used in chemical industries,such as sulfuric acid, alkali etc.

Product Parameter

Materials of Main Parts

Technical Specification