When conventional rubber O-rings, lip seals, and elastomeric profiles fail — because the process chemical attacks the rubber, the temperature exceeds the elastomer's range, or contamination from a rubber seal's leachable compounds is unacceptable — PTFE sealing profiles are the engineered solution. PTFE O-rings, V-rings (V-packing sets), D-rings, and custom extruded or machined profiles provide reliable sealing in the most demanding chemical, thermal, and regulatory environments that destroy conventional elastomeric seals.
Why PTFE Seals Instead of Rubber?
Rubber and elastomeric seals (Nitrile, EPDM, Viton, Silicone) are suitable for a wide range of service conditions, but they all have a characteristic that limits their use in critical applications: they are chemically reactive materials that can swell, shrink, harden, or leach plasticisers and accelerators into the process fluid they seal. PTFE has none of these weaknesses.
| Property | PTFE | Nitrile (NBR) | Viton (FKM) | EPDM |
|---|---|---|---|---|
| Max Temp (°C) | 260 | 120 | 200 | 150 |
| Min Temp (°C) | −200 | −40 | −20 | −45 |
| Acid resistance | Excellent | Poor | Good | Fair |
| Solvent resistance | Excellent | Good | Good | Poor |
| FDA compliance (virgin) | Yes | Some grades | Some grades | Some grades |
| Leachables | None | Plasticisers, accelerators | Minimal | Minimal |
| Compression set | High (cold flow) | Low | Low | Low |
The one area where rubber outperforms PTFE for sealing is compression resilience — rubber seals spring back when compressed; PTFE does not. This is why PTFE seals are typically used as energised seals (with a spring or elastomeric back-up ring that provides the compression force) rather than simple squeeze seals like standard rubber O-rings.
PTFE Sealing Profile Types
O-Rings
Round cross-section. Used in static and slow-dynamic applications with spring or elastomeric energiser. All standard AS568 and metric sizes available.
V-Rings (V-Packing)
V-shaped cross-section stacked in sets. Self-energising — fluid pressure pushes lips outward to seal. Widely used in valve stems, rotating shafts, and pump rods.
D-Rings
D-shaped cross-section for use in rectangular grooves. Better compression distribution than O-rings in some groove geometries. Common in valve bonnets and flange face grooves.
Square-Section Rings
Square cross-section for standard grooves where flat seating faces are preferred. More stable in groove than round O-rings under dynamic load.
U-Cups / Lip Seals
U-shaped cross-section for unidirectional dynamic sealing in hydraulic and pneumatic actuators. PTFE provides compatibility with water-based hydraulic fluids that destroy rubber.
Custom Profiles
Any cross-section manufactured to your drawing — T-shapes, L-shapes, cap seals, stepped profiles, and complex multi-function sealing elements.
Standard vs Custom PTFE Profiles
Standard PTFE O-Rings
We manufacture PTFE O-rings in all standard dimensions:
- AS568 series (American standard): Cord diameter 1.78 mm through 6.99 mm; all dash numbers from AS568-001 to AS568-932
- Metric series: Inner diameter 3 mm to 500 mm; cord diameter 1 mm to 10 mm
- DIN 3771 series for European equipment
PTFE V-Packing Sets
V-packing is supplied as matched sets (male adapter + female adapter + V-rings) in 3, 5, or 7 ring configurations. Custom ring counts for special applications. Common in:
- Gate valve, globe valve, and plug valve stem packing
- Pump shaft sealing in chemical and pharmaceutical service
- Hydraulic cylinder rod sealing with water-based fluids
- Autoclave and reactor vessel shaft seals
Custom Machined Profiles
For applications where no standard profile fits the groove geometry or sealing requirement, we machine custom PTFE profiles from rod or tube stock to your DXF drawing. Tolerances to ±0.05 mm on critical sealing dimensions. Custom profiles typically have a minimum order quantity — contact us with your drawing and required quantity for a quotation.
Applications by Industry
| Industry | Typical PTFE Seal Used | Reason for PTFE Over Rubber |
|---|---|---|
| Chemical processing | V-packing sets, O-rings in valve bonnets | Resistance to HCl, H₂SO₄, caustics, solvents |
| Pharmaceutical | O-rings, custom profiles in processing vessels | FDA compliance; no leachables; CIP/SIP compatible |
| Oil & gas | V-packing, O-rings in wellhead valves | H₂S resistance; wide temperature range |
| Cryogenic (LNG) | O-rings, lip seals at −160°C | Only material functional below −60°C |
| Semiconductor | Ultra-pure O-rings, custom seals | Zero metal ion or organic contamination |
| Food processing | O-rings, lip seals | FDA compliant; non-stick; cleanable |
Frequently Asked Questions
Why do PTFE O-rings need a spring or energiser?
Unlike rubber O-rings that spring back elastically when compressed, PTFE undergoes permanent cold flow (creep) under compression. Without something to maintain the sealing force over time, a PTFE O-ring will slowly extrude out of its groove and lose its sealing ability. An energised PTFE seal uses a stainless steel spring (coiled spring or cantilever spring) or an inner elastomeric core to continuously push the PTFE sealing lip against the mating surface, maintaining the seal regardless of creep.
Can PTFE O-rings be used in dynamic (moving) applications?
Yes, with appropriate design. PTFE's very low coefficient of friction makes it excellent for dynamic sealing — lower running friction than any elastomeric seal. Energised PTFE seals (spring-energised lip seals, PTFE U-cups, PTFE V-packing) are specifically designed for dynamic rod and shaft sealing in chemical, cryogenic, and pharmaceutical equipment. Pure PTFE O-rings without energiser are generally for static or very slow-oscillating service.
What PTFE grade is used for O-rings and sealing profiles?
Virgin PTFE is used for all chemical-contact and food/pharma sealing profiles. Chemically modified PTFE (TFM) is also used where slightly improved compression set characteristics are required. Filled grades are generally not used for O-ring profiles as the filler particles can create leak paths across the sealing interface on very soft groove surfaces.
PTFE Sealing Profiles — Standard & Custom
O-rings (AS568 and metric), V-packing sets, D-rings, custom profiles. Machined to drawing, all standard sizes in stock.
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