In addition to standard PTFE gaskets, Taifno also offers PTFE envelope gaskets. With over 20 years of industry experience, we possess comprehensive capabilities in R&D, manufacturing, and sales; our products are compatible with a pH range of 0–14, suitable for a wide temperature range, and offer cost-performance value.
PTFE envelope gaskets are composite sealing gaskets consisting of a PTFE outer jacket encapsulating a compressible filler core. The PTFE jacket provides universal chemical resistance (pH 0-14). The filler core provides compressibility, resilience, and conformability to flange irregularities.
The problem they solve: Standard PTFE gaskets are rigid and expensive. Rubber gaskets degrade in chemicals. Glass-lined flanges have uneven surfaces that standard gaskets cannot seal. Envelope gaskets solve all three.
|
Parameter |
Description |
|
Construction |
PTFE jacket slit from outer edge to inner bore; soft filler core inserted through slit |
|
Pressure |
Up to 4.0 MPa |
|
Size Range |
DN25-DN500 |
|
Key Feature |
Most economical, 30-50% less than solid PTFE |
|
Best For |
Low pressure, general chemical service, cost-conscious applications |
|
Parameter |
Description |
|
Construction |
Machined square cross-section; fully encapsulated filler core with no slit |
|
Pressure |
Up to 5.0 MPa |
|
Size Range |
DN25-DN500 |
|
Key Feature |
Full encapsulation — better sealing integrity; inner diameter can match flange bore to prevent flow turbulence |
|
Best For |
Medium-high pressure, critical chemical service, sealing integrity priority |
|
Parameter |
Description |
|
Construction |
PTFE tape folded and heat-sealed; corrugated metal insert (304/316 SS) inside |
|
Pressure |
Highest (above Type A/B) |
|
Size Range |
DN350+ (recommended) |
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Key Feature |
Corrugated metal core provides spring-back recovery and blowout resistance |
|
Best For |
High pressure, thermal cycling, large diameter flanges, blowout risk |
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Application Condition |
Recommended Type |
Reason |
|
Low pressure, general chemicals, cost priority |
Type A |
Most economical — 30-50% less than solid PTFE |
|
Medium-high pressure, sealing integrity priority |
Type B |
Full encapsulation, no slit, no exposed filler core |
|
High pressure, thermal cycling, large diameter |
Type C |
Metal core provides spring-back recovery and blowout resistance |
|
Industry |
Application |
Recommended Type |
|
Chemical Processing |
Pipe flanges, pump connections, reactor manways — acids, solvents, caustics |
Type A / B / C (pressure dependent) |
|
Glass-lined Equipment |
Glass-lined reactors, vessels, pipe flanges |
Type B / C |
|
Pharmaceutical |
Sterile equipment, bioreactors — FDA compliance |
Type B |
|
Food & Beverage |
Sanitary connections, filling equipment — FDA compliance |
Type A or B |
|
Oil & Gas |
Corrosive lines, wellhead equipment |
Type C |
|
Heat Exchangers |
Large diameter flanges, thermal cycling |
Type C |
|
FRP/Plastic Flanges |
FRP piping, plastic equipment flanges |
Type A / B |
Glass-lined flanges have wavy, uneven surfaces due to the glass coating process. Standard PTFE gaskets require high bolt torque to seal — which cracks the brittle glass layer.
Envelope gaskets solve this:
Low torque sealing — prevents glass cracking
Conformability — compensates for wavy, uneven surfaces
PTFE jacket — handles aggressive media
Compressible core — absorbs flange irregularities
PTFE jacket resists almost all chemicals across pH 0-14, strong acids, alkalis, solvents, hydrocarbons, chlorine, and more. The filler core is fully protected and never contacts the media.
Envelope gaskets seal at significantly lower torque than solid PTFE gaskets — protecting fragile glass-lined and plastic flanges from damage.
The compressible core compensates for wavy surfaces, scratches, pitting, flange distortion, and warping.
Type A envelope gaskets cost 30-50% less than solid PTFE gaskets of the same size, delivering chemical resistance at a fraction of the cost.
PTFE jacket meets FDA 21 CFR 177.1550. Food-grade filler cores available for food and pharmaceutical applications.
A: A PTFE envelope gasket consists of a PTFE outer jacket encapsulating a compressible filler core. The PTFE jacket provides universal chemical resistance (pH 0-14, up to +200°C) while the filler core provides compressibility and resilience.
Use envelope gaskets when: You need chemical resistance on uneven or glass-lined flanges, you require low torque sealing to protect fragile surfaces, you need cost-effective chemical resistance (30-50% less than solid PTFE), or you need FDA-compliant materials for food/pharma applications.
When NOT to use: Extreme high pressure (use metal jacketed), high temperature steam above +200°C, or applications requiring absolute chemical purity with no filler core (use solid PTFE).
A: Three types for three different applications:
Type A (Slit): Most economical (30-50% less than solid PTFE). Pressure up to 4.0 MPa. Best for low-pressure general chemical service.
Type B (Machined): No slit, fully encapsulated filler core. Pressure up to 5.0 MPa. Inner diameter can match flange bore to prevent flow turbulence. Best for medium-high pressure critical chemical service.
Type C (Folding): Corrugated metal core provides spring-back recovery and blowout resistance. Recommended for DN350+. Best for high pressure, thermal cycling, large diameter flanges, and blowout risk.
Quick rule:
Economy + low pressure → Type A.
Sealing integrity + medium-high pressure → Type B.
High performance + large diameter → Type C.
A: Temperature: Up to +200°C (PTFE limit — filler may limit lower depending on core material).
Pressure: Type A up to 4.0 MPa, Type B up to 5.0 MPa, Type C highest.
Chemical: pH 0-14 universal resistance, not compatible with molten alkali metals or elemental fluorine at high temperatures.
Three common mistakes:
(1) Over-tightening on glass-lined flanges: envelope gaskets seal at lower torque than solid PTFE; excessive compression damages the PTFE jacket and can crack glass linings. Use a torque wrench and follow flange manufacturer specifications.
(2) Using Type A in high-pressure service: above 4.0 MPa, the gasket may deform or fail; use Type B or C.
(3) Not retightening after temperature changes: PTFE has thermal expansion/contraction; for operating temperatures above 100°C, retighten bolts at room temperature. We include installation specifications with every order.
