R. Bruce Hopkins, Ph.D., RE.
The Hopkins Engineering Co., RC.
Cedar Falls, Iowa
17.1 ELASTOMERIC SEAL RINGS / 17.1
17.2 SEALS FOR ROTARY MOTION / 17.4
17.3 SEALS FOR RECIPROCATING MOTION / 17.9
REFERENCES / 17.15
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. 17.1«. 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 17.!.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 Jl2Oa 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. 17.Ib is manufactured by cutting lengths from
a tube of molded material. The standard sizes listed in SAE J120a are summarized in
Table 17.2. 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 [10.3 newtons per square millimeter (N/mm2)].
The standard shape of groove for sealing rings is shown in Fig. 17.2. The actual
groove dimensions depend on the