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Piston Ring Types
Scraper Rings

Practically all of the scraper rings used are rings with a step recessed into the bottom outer face. This assures extremely effective oil scraping [2].
The efficient scraping can be explained by a number of features. The step increases the unit pressure. Additionally, the step relief causes a positive twist which, without gas pressure, brings the periphery into bore contact only with the very edge of the step.
The volume created by the step is beneficial in allowing large amounts of oil to be stored there. This means that the favourable characteristics of a ring with a stepped bottom outer edge can be adjusted by varying the size of the step.
The step can be produced in a rectangular or undercut (Napier) design. An advantage of the undercut step is that, when the ring twists, a sharp downward scraping edge will still be available to conduct the oil quickly from the outer edge of the ring into the reservoir of the step and thus prevent oil from gathering at the scraping edge and diminishing the scraping effect.
If necessary, the benefit of the oil storage volume can be enhanced by the provision of an additional recess on the outer diameter of the bottom piston groove side.
Rings with a step have a higher oil scraping effect than taper faced rings, but this is usually coupled with higher blowby.

The following types exist:

Napier Ring:
This can be installed in the second groove in passenger car gasoline and passenger car and truck diesel engines, but has been almost entirely replaced by the taper faced Napier ring. It is now occasionally used only in the compressors of air brake systems.

Taper Faced Napier Ring:
Like on the taper faced ring, the periphery of this ring is designed with a taper in order to improve oil scraping and quicken running-in. These rings are used on the same applications as Napier rings.

Taper Faced Closed Gap Scraper Ring::
On this ring the step runs out at the gap and is designed without an undercut. It seals better against blowby than the Napier and taper faced Napier rings with a continuous step. The applications for this ring are the same as for Napier and taper faced Napier rings.


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