Seal rings of the O-ring type are used as both static and dynamic seals. Static seals serve the same purpose as gaskets; that is, they provide a seal between two members that are not intended to undergo relative motion. Dynamic seals, however, are used where rotating or reciprocating motion is intended to occur | CHAPTER 17 SEALS R. Bruce Hopkins . . The Hopkins Engineering Co. P. C. Cedar Falls Iowa ELASTOMERIC SEAL RINGS SEALS FOR ROTARY MOTION SEALS FOR RECIPROCATING MOTION REFERENCES ELASTOMERIC SEAL RINGS Seal rings of the O-ring type are used as both static and dynamic seals. Static seals serve the same purpose as gaskets that is they provide a seal between two members that are not intended to undergo relative motion. Dynamic seals however are used where rotating or reciprocating motion is intended to occur. O-rings are molded to the size of the elastomeric material with a circular cross section as shown in Fig. . The size is designated by the cross-sectional diameter w and the nominal inside diameter ID . The standard sizes specified in SAE J120a are summarized in Table . The first size number in a group is associated with the minimum inside diameter and the last size number is associated with the maximum inside diameter. Some manufacturers provide additional sizes that extend the range of inside diameters for a particular cross-section size. The nominal inside diameters were selected to provide dynamic seals in cylinder bores dimensioned in inches and common fractions of inches. Either SAE J120a or manufacturers recommendations should be consulted to obtain the recommended compression of the cross section. The compression is different for static and dynamic applications. The rectangular-section ring in Fig. is manufactured by cutting lengths from a tube of molded material. The standard sizes listed in SAE J120a are summarized in Table . The first size number in a group is associated with the minimum inside diameter and the last size number is associated with the maximum inside diameter. Rectangular-section rings are suitable for static applications with pressures up to 1500 psi newtons per square millimeter N mm2 . The standard shape of groove for sealing rings is shown in Fig. . The actual
