PTFE-Lined Butterfly Valve

Valves / Butterfly Valve

A PTFE-lined butterfly valve features a ductile iron body internally lined with PTFE (polytetrafluoroethylene), combining the compactness and economy of a butterfly valve with the chemical resistance of PTFE for handling highly corrosive fluids at moderate pressures and temperatures.

Working Principle

The disc rotates 90 degrees within the PTFE-lined body bore. The PTFE liner covers all wetted surfaces, providing universal chemical resistance. When the disc closes, it compresses against the PTFE seat area of the liner for shut-off. The PTFE liner is mechanically locked into the body casting by dovetail grooves or pins, preventing movement or collapse under pressure. The disc itself may be PTFE-coated or made from solid PTFE for maximum chemical purity. Operating torque is low due to PTFE's self-lubricating properties.

Key Components

Ductile iron body with PTFE liner, PTFE-coated or solid PTFE disc, stainless steel shaft, PTFE packing, hand lever or gear operator.

Types & Variants

Type	Key Feature	Typical Use
Wafer PTFE-lined butterfly	Wafer body, PTFE liner	Chemical plant corrosive isolation
Lug PTFE-lined butterfly	Lug body, dead-end capable	Corrosive dead-end service
Double-offset PTFE-lined	Double-offset + PTFE liner	Higher pressure corrosive service
Vent-lined PTFE butterfly	Liner vent for vacuum service	Corrosive vacuum process

Common Materials

Body: ASTM A395 ductile iron. Liner: virgin PTFE for maximum purity, or filled PTFE for creep resistance. Disc: 316SS with PTFE coating, or solid PTFE. Shaft: 316SS. Packing: PTFE. Bolting: ASTM A193 B7 or B8M for corrosive atmospheres.

Applicable Standards

API 609 (butterfly valves, reference)
MSS SP-98 (PTFE-lined valves)
ASTM F1545 (PTFE-lined piping components)
ASME B16.1 (flanged ends, ductile iron)

Industrial Applications

Chemical manufacturing (acids, halogens, caustics)
Chlor-alkali plants
Pharmaceutical processing
Semiconductor ultra-pure chemical handling
Metal finishing and electroplating
Pulp and paper bleach plants

Advantages & Disadvantages

Advantages

Universal chemical resistance from PTFE liner
Low operating torque (PTFE self-lubricating)
Compact butterfly design saves space vs. PTFE-lined gate or globe valves
Lower cost than alloy valves (Hastelloy, titanium) for equivalent corrosion resistance
No process fluid contamination

Disadvantages

Temperature limited to about 200C (PTFE cold-flows above this)
Pressure limited to Class 150 (ductile iron body)
PTFE cold-flow under sustained seat load causes progressive leakage
Not fire-safe (PTFE decomposes above 260C)
Vacuum service can collapse liner unless vented design is used

Selection Guide

Glass-filled PTFE liners resist cold-flow better than virgin PTFE at the cost of some chemical purity
For vacuum service, specify vented liner design to prevent collapse
PTFE-lined butterfly valves are not fire-safe and cannot pass API 607 — do not specify for hydrocarbon fire-safe service
Limit flow velocity to 3 m/s to prevent liner erosion

Practical Tips

PTFE cold-flow is the primary failure mode for lined butterfly valves — the seat area gradually deforms under disc contact pressure, and a valve that was tight at installation may leak within months on high-pressure service
A PTFE-lined butterfly valve costs 60-70% less than a Hastelloy butterfly valve for the same chemical service — the trade-off is temperature and pressure limitation

FAQ

Can PTFE-lined butterfly valves handle vacuum?

Only with vented liner design. Without venting, vacuum on the process side can collapse the PTFE liner inward, destroying the seal and blocking flow. Always specify vented liners for vacuum service.

PTFE-lined butterfly vs PTFE-lined gate valve?

Butterfly: more compact, lower cost, lower pressure drop. Gate: tighter shut-off, higher pressure rating, less cold-flow leakage. Choose butterfly for general corrosive isolation; choose gate for zero-leakage or higher-pressure requirements.