Tri-Clamp PTFE Envelope Gasket (PTFE with Viton Filler)
ABOUT THIS PART
PTFE envelope tri clamp gasket with a Viton core, FDA compliant, in 1, 1.5, 2, 4 and 6 inch, from $6.50.
Also sold as PTFE encapsulated Viton. This is the best overall gasket on this site and the one we point most buyers at.
PTFE chemistry with spring-back. The envelope gives the chemical resistance, including isopropyl, where Viton fails. The Viton core gives it the recovery solid PTFE does not have, so the joint reseals instead of taking a set.
Sizes and price
| Size | Price |
|---|---|
| 1 in | $6.50 |
| 1.5 in | $6.95 |
| 2 in | $6.50 |
| 4 in | $15.50 |
| 6 in | $59.50 |
We price these as competitively as we can against what the same gasket sells for elsewhere. These are standing prices, not a promotion. The 6 inch is the size a 20 LB system runs 22 of.
The numbers
- Temperature: -100 F to 400 F (-73 C to 204 C), continuous static use
- Clamp torque: 50 in-lb, the rigid figure. An elastomeric gasket takes 30
- Compliance: FDA compliant
- Excellent on: butane, propane, ethanol, heptane, pentane, hexane and isopropyl
Which material for which job
| Material | Temperature | Torque | Pick it when |
|---|---|---|---|
| PTFE envelope, Viton core | -100 F to 400 F (-73 C to 204 C) | 50 in-lb | Isopropyl, cold service, or a joint broken every run |
| Solid PTFE | -350 F to 500 F (-212 C to 260 C) | 50 in-lb | Isopropyl or cold service on a joint that stays made up. Cheaper |
| Viton (FKM) | -40 F to 400 F (-40 C to 204 C) | 30 in-lb | The hydrocarbon default. Not for isopropyl |
| Buna-N | -30 F to 250 F (-34 C to 121 C) | 30 in-lb | Water, food, general sanitary. Cheapest |
| Silicone | -85 F to 450 F (-65 C to 232 C) | 30 in-lb | Steam and food. Severe on every hydrocarbon |
Two cases send you here: isopropyl service, where Viton rates severe, and anything running colder than Viton's -40 F (-40 C) limit.
The cold end, and what actually limits it
Minimum solvent temperature on an N.B. Oler system is -40 F (-40 C) on standard elastomeric gaskets, and -65 F (-54 C) with PTFE. Both figures come from 3P Certz and were confirmed in September 2026. On the cold end of a run the gasket is the limiting component, not the vessel, so check the gasket against your lowest process temperature rather than against the vessel rating.
Where this one sits
- This gasket is our first recommendation across the range. PTFE against the process and a Viton core behind it, rated -100 F to 400 F (-73 C to 204 C) as a material, and it is what takes an N.B. Oler system to its -65 F (-54 C) minimum solvent temperature.
- Viton remains the default on a hydrocarbon system and it is what we run in our own shop, rated -40 F to 400 F (-40 C to 204 C). Note that -40 F and -40 C are the same temperature, which is why both units read -40.
- In our own operating experience Viton gives the best results in cold service of the elastomers we have used. That is shop experience rather than a laboratory result. This envelope gasket is the step up from it, for the coldest work and for isopropyl.
Replacement and quantities
- Replace every 3 to 6 months regardless of how it looks
- Replace immediately on any cracking, tearing, splitting or permanent deformation
- A gasket that has taken a compression set passes a cold leak check and then weeps once the line comes up to pressure. That is why interval beats inspection on a gasket
- A 20 LB system takes 22 six inch gaskets. A 40 LB takes 44
- Full comparison: Choosing the right gasket material for tri-clamp connections
Stocked in Bend, Oregon, and it usually ships the same day.
SPECIFICATIONS
▦ IN YOUR MANUAL
This part appears in the operator manual that ships with your system. The QR code there links to this page.
◈ REFERENCE FOR THIS PART
COMMON QUESTIONS
What is the Viton core for?
The PTFE envelope gives the chemical resistance. The Viton core inside gives it spring-back, so the joint reseals instead of taking a set. That is the difference between this and a solid PTFE gasket.
When do I need this instead of Viton?
Isopropyl service, where Viton rates severe, and the coldest work, below Viton's -40 F (-40 C) rating. It is also our first recommendation generally, because it is the best overall gasket on this site. Viton remains the default on a hydrocarbon system and the one we run in our own shop, and in our own operating experience it gives the best results in cold service of the elastomers we have used.
Is this the same as PTFE encapsulated Viton?
Yes, the same part. PTFE envelope, Viton filler, PTFE encapsulated Viton, all the same gasket.
What temperature can it take?
-100 F to 400 F, which is -73 C to 204 C, for continuous static use.
What do they cost?
1 in $6.50, 1.5 in $6.95, 2 in $6.50, 4 in $15.50 and 6 in $59.50. Those are standing prices, set as competitively as we can against what the same gasket sells for elsewhere, not a promotion.
Envelope or solid PTFE?
Solid PTFE is cheaper and right for a joint that stays made up. The envelope is for a joint broken every run, because it recovers instead of taking a set.
Why is the torque different from Viton and Buna-N?
This is a rigid gasket, so it takes 50 in-lb against 30 for an elastomeric one. Torquing a rigid gasket to elastomeric spec will leak, and torquing an elastomeric gasket to rigid spec destroys it.
How often should these be replaced?
Every 3 to 6 months regardless of appearance, and immediately on any cracking, tearing, splitting or permanent deformation.
How many does a system take?
A 20 LB system takes 22 six inch gaskets and a 40 LB takes 44.
Is it FDA compliant?
Yes.