The sinuses are air-filled cavities. 1  They are located: 2  Within the bony structure of the cheeks. 3  Behind the forehead and eyebrows. 4  On either side of the bridge of the nose. 5  Behind the nose directly in front of the brain.
An O-ring is a round ring that is used as a gasket for sealing a connection. O-rings are typically constructed out of polyurethane, silicone, neoprene, nitrile rubber or fluorocarbon. These rings are commonly used in mechanical applications, such as pipe connections, and help to ensure a tight seal between two objects. O-rings are designed to be seated in a groove or housing that keeps the ring in place. Once in its track, the ring is compressed between the two pieces and, in turn, creates a strong seal where they meet.
O-rings function in so many applications because there is a diverse scope of material used in their fabrication. Many are made from rubber, or, more specifically, elastic polymers, or elastomers. These polymers are cured, often through vulcanization, resulting in a strong, durable and more elastic rubber. EPR o-rings work well with Skydrol and other hydraulic fluids, as well as steam, water, silicone oils, brake fluids and alcohols. 2  Deficiencies: Similar to nitrile, EPR is not perfect for a wide-range of applications due to wear and tear issues.