Silicone FDA USP Class VI Clamp Gasket
Rubber Fab materials and chemical compatibility guide
Tubes Technologies gasket selection guide
Rubberfab references, Type I gasket without lip
Rubberfab references, Type II gasket with lip
Guidelines for sanitary gasket materials
On a tri-clamp connection, sealing is not provided by the clamp but by the gasket. The clamp sets the compression; the gasket turns it into a seal and absorbs the forces from the line. The choice of its material determines the allowable temperature, chemical compatibility and service life of the connection.
Platinum-cured silicone, -40 °C to +232 °C, without lip and with lip
Platinum-cured silicone sanitary tri-clamp gasket, available without lip (Type I) and with centring lip (Type II). Service range from -40 °C to +232 °C. Very flexible, it seals on misaligned faces where a rigid material leaks. FDA and USP Class VI compliant, low extractables. Diameters from 1/2″ to 12″.
Where this material is the right choice, and where it is not
Platinum-cured silicone is the material of choice on sanitary water circuits when PTFE is not an option, either because of severely misaligned fittings or when the cost of the high-pressure clamps required for PTFE is not justified. Its flexibility allows it to seal where a rigid material would leak. Its platinum curing gives it a very low extractables and leachables profile, valued in pharmaceuticals. Excellent resistance to high and low temperatures.
Silicone has poor resistance to certain chemical agents, solvents and oxidising agents, and degrades in the presence of oxygen at high temperature. Mechanically, it has low tear and abrasion resistance, which limits its service life at points that are dismantled very frequently. It has neither the chemical resistance of PTFE nor the oil resistance of FKM. It is a gasket for flexibility, not for chemical resistance.
Type I and Type II: the lip changes installation
Type I, or Type B, is a flat gasket without lip. It is centred by hand in the groove of the two ferrules. This is the most common and least expensive version.
Type II, or Type A, has a centring lip that fits into the inside diameter of the ferrule. The gasket positions itself, cannot shift while the clamp is being closed, and alignment of its inner face with the flow path is guaranteed. On lines where a shifted flat gasket creates retention, or on hard-to-reach installations, the lip eliminates the risk of poor centring.
The choice between the two does not depend on the material, which is identical, but on the centring requirement at the installation point. Both versions cover the same temperature range and the same chemical compatibility.
Material properties
| Characteristic | Value |
| Material | Platinum-cured silicone |
| Service temperature | -40 °C to +232 °C (-40 °F to 450 °F) |
| Curing | Platinum, low extractables and leachables |
| Flexibility | The highest in the range, misaligned assemblies |
| Compliance | FDA, USP Class VI, depending on size (see appendix) |
| Versions | Type I without lip, Type II with centring lip |
The temperature range and chemical compatibilities come from the manufacturer’s data. Detailed fluid-by-fluid chemical information is provided in the materials guide and the compatibility sheet, available for download.
Dimensions
Standardised dimensions, common to all tri-clamp gasket materials. The gasket outside diameter corresponds to the ferrule face, the inside diameter to the flow path. A gasket whose inside diameter protrudes into the flow path creates retention; a gasket that is too small opens a crevice.
| Size | Gasket ID (mm) | Gasket OD (mm) | Ferrule flange A (mm) | Tube DN |
| 1″ | 22,9 / 0.900″ | 50,4 / 1.984″ | 50,5 | DN25 |
| 1 1/2″ | 35,6 / 1.400″ | 50,4 / 1.984″ | 50,5 | DN40 |
| 2″ | 48,3 / 1.900″ | 63,9 / 2.515″ | 64 | DN50 |
| 2 1/2″ | 61,0 / 2.400″ | 77,5 / 3.050″ | 77,5 | DN65 |
| 3″ | 73,7 / 2.900″ | 90,9 / 3.579″ | 91 | DN65 |
| 4″ | 98,3 / 3.869″ | 118,9 / 4.682″ | 119 | DN100 |
| 6″ | 147,8 / 5.817″ | 165,3 / 6.507″ | 167 | DN150 |
Millimetre conversions are for guidance only, based on the manufacturer’s dimensions in inches. The complete clamp, ferrule and tube correspondence table is available for download.
The gasket: the sensitive link in the clamp fitting
The quality of a clamp connection depends on three elements: the gasket, the clamp and pipe alignment. The gasket provides the seal and at the same time absorbs the torsional forces transmitted by the line. This dual role is the weak point of the clamp fitting.
A misaligned or stressed section makes the gasket work constantly, causing wear and then premature tearing. Excessive tightening pushes the gasket into the flow path and creates a dead leg. Compression is achieved at the torque specified for the clamp, never by feel. The gasket is the consumable part of the connection: it is replaced, not salvaged.
This material compared with others
A gasket material is chosen based on temperature, fluid, dismantling frequency, regulatory requirements and cleaning method. Here is what sets the main materials apart.
| Material | What it offers | Its limitations |
| EPDM (and silicone) | Very flexible, seals even on irregular surfaces, easy to install, economical | Limited temperature, sensitive to solvents and oxidisers, does not withstand oils |
| FKM Viton | Solvents, oils, acids, up to 204 °C, ozone-resistant | Less effective with strong oxidisers, less flexible, more expensive |
| Solid PTFE | Exceptional chemical and thermal resistance | Very rigid, high tightening, possible creep |
| EPDM/PTFE enveloped | Inert PTFE face, flexible EPDM core, good compromise | Creep if overtightened, EPDM core limited in temperature |
| Gylon 3504 | Flexible, low tightening, creep-resistant, -260 to +268 °C | Flat without lip, care required during installation, blue |
| Tuf-Flex | PTFE bonded to EPDM, crush-resistant, WFI | More expensive, strong oxidisers to be checked |
| Tuf-Steel | PTFE + 316L stainless steel, creep-resistant, -196 to +288 °C | Expensive, reserved for demanding applications |
Each material has a dedicated data sheet with its service ranges, compliance and detailed chemical compatibilities.
Frequently asked questions
Silicone or PTFE?
Silicone when faces are misaligned or when PTFE would require expensive high-pressure clamps. PTFE when chemical inertness is the priority and the line is well aligned. Silicone seals through flexibility, PTFE through inertness.
Type I or Type II?
Type I, without lip, for standard installation. Type II, with centring lip, when the gasket must position itself and not shift, particularly where access is difficult or at points where shifting creates retention. Same material, same range; only the centring differs.
How do I choose the size?
On the outside diameter of the ferrule, like the clamp. The gasket inside diameter must be flush with the flow path without protruding. The correspondence table gives the equivalence between size, ferrule and tube.
Which compliance applies for pharmaceuticals?
FDA and USP Class VI compliance is stated by the manufacturer for sizes 1″ to 4″. Outside this range, it must be verified before being recorded in a file. The exact certification must appear on the material certificate for the batch delivered.