Very good and interesting video about O-rings from Tarkka
Video description:
O-rings are the epitome of elegant engineering: The ring itself costs only a few cents, and the groove it goes in is simple and easy to manufacture. But despite this simplicity, the resulting seal is able to reliably hold many thousands of psi of pressure. O-rings are definitely a machine design component you’ll want to be familiar with, and in this video, we’re going to tell you all about how to design seals with them