Types of Rubber Gaskets

A full-face gasket extends to the outer diameter of the flange and covers the bolt holes. The bolt passes through both flange and gasket. This design protects the entire flange face from the media and distributes bolt load over the largest possible area.

Full-face gaskets are common on low-pressure cast-iron and plastic flanges where flange stiffness is lower and the extra gasket area helps prevent distortion. They use more material than ring gaskets but are more forgiving of uneven bolt preload.

A ring gasket is an annular seal that sits inside the bolt circle, leaving the bolt holes exposed. It is used on raised-face and flat-face steel flanges where the sealing surface is confined to the area around the bore.

Ring gaskets use less material and are easier to center during assembly. They are the default for ASME B16.21 Class 125/150 steel flanges and similar DIN/EN designs.

An envelope gasket wraps a thin PTFE skin around a soft core such as EPDM, FKM or compressed fiber. The PTFE faces provide chemical resistance while the core provides conformability and recovery.

Envelope gaskets are common on glass-lined flanges, chemical reactor nozzles and other applications where the media attacks standard elastomers but the flange cannot tolerate a solid PTFE gasket.

Strip gaskets are long, narrow sections cut from sheet stock, used for door seals, enclosure frames and large perimeter joints. Sheet gasket material is the raw stock from which flat gaskets are punched or cut.

Both forms are economical for MRO and in-house fabrication. The user cuts the final shape on site, so tolerance and finish depend on the shop equipment.

Any 2D profile that does not fit the categories above falls into custom-cut gaskets. These are produced by die-cutting, waterjet or flashcut from drawing. Custom profiles include irregular equipment covers, manway seals with bolt-hole tabs, and gaskets with internal cutouts.

Custom gaskets are specified by drawing rather than by standard catalog number.

ASME B16.21 covers non-metallic flat gaskets for pipe flanges, including dimensions for Class 125 and 150 cast-iron and steel flanges. DIN EN 12560 defines dimensions for non-metallic flat gaskets in metric flange systems. The gasket supplier cuts to these templates or to the equipment drawing.