The kind of piston ring associated with the combustion engine can also be found in mechanical engineering. As a piston seal installed in a hydraulic cylinder, it has the advantage of showing very little wear and also being able to slide over bores (Figure K 18).
On the negative side, the piston ring's lack of suppleness as a contact seal means it has practically the same effect as a gap seal, i.e. it is never possible to achieve a complete seal with it — not least because of the inevitable impact involved. The seal effect can be improved, however, if the impact occurs at an angle or in stages and by installing more than one ring.
Figure K 18: Piston rings