Trunnion mounted ball valves are selected for full-bore isolation service in high-pressure, large-bore pipeline and process applications where floating ball designs are not suitable due to high operating torque, seat load, and differential pressure requirements. The trunnion support transfers pipeline pressure loads from the seats to the trunnion bearings, reducing seat wear and operating torque — making trunnion mounted designs the standard specification for transmission pipelines, compressor stations, and critical isolation duty at Class 600 and above to API 6D. Spring-loaded seats provide constant sealing contact against the ball under all operating conditions, enabling reliable bidirectional shut-off and self-relieving cavity over-pressure protection — critical safety features for high-pressure gas and liquid hydrocarbon pipeline service. Full-bore design ensures unrestricted flow and pigging tool passage for inline inspection and cleaning operations without valve removal, mandatory for transmission pipeline service under API 6D requirements. Body material selection covers a wide range of service conditions — carbon steel (WCB) for standard pipeline service, low-temperature carbon steel (LCB) for cold climate and cryogenic applications, alloy steel (WC6) for high-temperature service, and stainless steel (CF8M) or duplex grades for corrosive and sour gas environments. Gear operators are standard for large-bore and high-pressure sizes, with electric, pneumatic, and hydraulic actuators selected for automated control, ESD duty, and remote operation requirements. Design standard API 6D governs trunnion mounted ball valves for pipeline service, with ISO 17292 as the international equivalent.