One-piece screw pins and clipscommonly hold footed seals in place. Adhesives and mechanical interference fits can also be used. One-piece retainerScrew pinClips seal is inflated to deliver thenecessary travel.For extra heavy or unevenloads and rough mating sur- faces, sealing pads are often placed atop any of the seals mounted in grooves or chan- nels.

AIR CONNECTIONS

Most seals need only one airconnection and it can be built into the base or the end, de- pending on requirements. More connections may be needed for faster cycling, to hold large seals in place, or when inflating seals with a fluid.

SPECIAL ISSUES

Cutting corners: A lot of in-flatable seals run around cor- ners and they usually won’t rise to their full travel height unless the bend radius is gen- erous. And some seals must be made to work on preexist- ing openings with sharp cor- ners.As a general rule for out-ward radial seals, corner radii should be at least four to eight times the relaxed height of the seal. For inward radial seals, corner radii should be There are also several otherissues that commonly arise with inflatable gaskets. Be aware of these as you proceed with your design.

RETENTION

There are several ways tohold footed inflatable seals in place. The simplest is to snake the seal through a series of passivated aluminum or stain-less-steel clips. This works on both curved and irregular sur- faces. Adhesives can also be used rather than clips. For straight seals, a variety of ex- trusions provide strong mounting points. And straight snap seals are best held in place by form-fitted extru- sions. Passivated aluminum or stainless steel should be used for components that touch the seals.To retain seals in grooves,size the grooves to the width of the seal itself plus the toler- ance. Following this sizing rule for circular seals that expand outward or inward radially, es- pecially smaller diameters, creates enough compression forces to hold the seal in place. Other configurations generally use adhesives.

MATERIALS

Several hollow interlockingseals can be combined with a mechanicalinterlockto create a circular seal fromlong straight sections.But joint sections may notrise as high when inflatedcompared to the rest of the seal. Inflatableseals are made out of all the principle elas- tomers and re- inforcing ma- terials. EPDM (ethylene propylene di- monomer) is by far the most widely used elastomer, based on itsperformance and price. All the elastomers can be molded or extruded.Seal materials can be com-bined to meet special require- ments. Adding a layer of Viton over EPDM, for example, en- hances chemical resistance. And a copper mesh over EPDM creates a conductive seal suit- able for EMI isolation on a ma- chine cabinet or to shield an entire room. A heating element used with a silicone seal can keep the seal flexible down to –60°F.