The concepts oil transport and leakage are often used, but the meanings of the concepts differ since they express personal judgements emanating from the different demands on the cylinder.
A certain oil transport is needed to provide the necessary lubrication of the rod seal, guide and wiper. The lubrication film must, however, be thin enough not to leave the rod but to return into the cylinder at the return stroke.
The lubrication film’s limited amount of oil transported during the reciprocating movement, passing wiper seal, guide and rod seal and leaving a slight oil ring and without dripping, is normally defined as oil transport.
The amount of lubrication film wiped off by the wiper seal (together with the contamination particles that may be present) must not cause substantial oil rings or drops. Repeated dripping is normally defined as leakage.
The amount of oil transport or leakage is directly proportional to the area of the surface wiped off.