Description Description Freudenberg Sealing Technologies (formerly Tobul) O ring seal (Buna-N) used with piston accumulator series 9A30 is a mechanical gasket with a round cross-section. They are made from elastomer materials and used in various fluid applications to form a leak-proof seal between two parts. O-rings are installed into a machined or molded grove on a part surface; when the two parts are joined, it compresses the o-ring and deforms the cross-section, creating a tight seal. State of California Proposition 65 WARNINGCancer and Reproductive Harm - www.P65Warnings.ca.gov. Literature & Docs Accessories