PTFE-Lined Gate Valve

Valves / Gate Valve

A PTFE-lined gate valve features a ductile iron or carbon steel body internally lined with PTFE (polytetrafluoroethylene), providing excellent chemical resistance for handling highly corrosive fluids such as strong acids, caustics, and halogens at moderate temperatures and pressures.

Working Principle

The valve body and bonnet are manufactured from ductile iron or carbon steel for structural strength. The internal surfaces in contact with the process media — body bore, seat area, and gate faces — are lined with PTFE, typically 3-5mm thick, which is locked into place by mechanical interlocks in the body casting. The gate itself is also PTFE-lined or made from solid PTFE. When the gate descends, PTFE surfaces on the gate press against PTFE seat faces to create a chemically inert seal. The stem passes through a PTFE packing gland. Because PTFE is a soft, low-friction material, operating torques are relatively low.

Key Components

Ductile iron or carbon steel body, PTFE liner (locked in), PTFE-lined gate, stem (SS or coated), PTFE packing, handwheel, bonnet bolts.

Types & Variants

Type	Key Feature	Typical Use
Flanged PTFE-lined gate	Flanged ends, ductile iron body	Chemical plant isolation
Wafer PTFE-lined gate	Wafer-style, compact	Retrofit between flanges
Vent-lined gate	Liner vent hole in body	Prevents liner collapse on vacuum

Common Materials

Body: ASTM A395 ductile iron or ASTM A216 WCB carbon steel. Liner: virgin PTFE (unfilled) for maximum chemical purity, or filled PTFE (glass-filled) for improved creep resistance and temperature capability. Stem: AISI 304 or 316 stainless steel. Packing: PTFE or PTFE-impregnated graphite. Bolting: ASTM A193 B7 with 2H nuts standard; B8/8M for corrosive atmospheres.

Applicable Standards

API 603 (corrosion-resistant cast gate valves, reference)
MSS SP-98 (PTFE-lined valves)
ASME B16.1 (flanged ends, ductile iron)
ASME B16.5 (flanged ends, steel)

Industrial Applications

Chemical manufacturing (sulfuric, hydrochloric, hydrofluoric acids)
Chlor-alkali plants (chlorine, caustic soda)
Pharmaceutical processing (high-purity corrosive media)
Metal finishing and plating (chromic, nitric acids)
Semiconductor manufacturing (ultra-pure chemicals)

Advantages & Disadvantages

Advantages

Outstanding chemical resistance — PTFE resists virtually all industrial chemicals below 200°C
Low friction — easy operation with low torque
No contamination of process fluid — ideal for high-purity service
Lower cost than exotic alloy valves for the same corrosion resistance

Disadvantages

Temperature limited to about 200°C (PTFE cold-flows above this)
Pressure limited to Class 150 (ductile iron body) or Class 300 (steel body)
PTFE liner can cold-flow under sustained pressure, causing seat leakage
Vacuum service can collapse the liner unless vented design is used
Not fire-safe — PTFE decomposes above 260°C

Selection Guide

For vacuum service, always specify a vented liner design to prevent collapse
Glass-filled PTFE liners resist cold-flow better than virgin PTFE but sacrifice some chemical purity
If fire-safe certification is required, PTFE-lined valves cannot meet API 607/FM fire test requirements
Maximum velocity through the valve should be limited to 3 m/s to prevent liner erosion

Practical Tips

PTFE cold-flow is the silent killer of lined valves — the liner gradually deforms under seat load, and a valve that passed seat testing at installation may leak within months on high-pressure service
Never use PTFE-lined valves on slurries or abrasive media — PTFE is extremely soft and erodes rapidly

FAQ

What is the maximum temperature for a PTFE-lined gate valve?

The practical maximum continuous service temperature is about 200°C. PTFE begins to cold-flow significantly above this temperature, and the material decomposes above 260°C.

Can PTFE-lined gate valves be used on vacuum?

Only with a vented liner design. Without venting, vacuum on the process side can collapse the PTFE liner inward, destroying the seal and possibly blocking the flow path.