Mechanism: a spring-loaded lip riding on a thin film of lubricant, not a static gasket
The device's job is dynamic, not passive: "its primary function is to achieve dynamic sealing by retaining essential lubricants, such as oil or grease, within a machinery assembly while simultaneously preventing the ingress of external contaminants like dirt, dust, and moisture." The physical contact that does the work is "the primary sealing lip, which is the dynamic barrier, [and] is molded to press against the shaft at a precise angle, forming a narrow contact zone known as the sealing line," and that contact stays loaded because "a circular coil spring, called a garter spring, is fitted around the circumference of the sealing lip to maintain a consistent radial force against the shaft." The lip does not run dry against the shaft: "when the shaft begins to rotate, a minute layer of lubricant is drawn into the contact zone, separating the lip from the shaft surface" — on more advanced lip designs, "angled micro-grooves generate a pressure gradient that actively pumps any lubricant attempting to leak out back toward the fluid side of the seal." A separate source confirms the basic geometry: "the seal construction consists of a sprung main sealing lip which has a line contact with the shaft," with the sealing profile's "two angles... varied to create a pressure distribution at the seal contact line which has a steeper slope on the oil side of the seal," and, separately, "in order to exclude contaminants numerous types of dust lips or exclusionary lips may be used" — the dust lip catalogue SKUs list as a distinct construction feature from the primary sealing lip.
