Trunnion Ball Valve — Support Plate

Most trunnion mounted ball valves anchor the ball through external shaft extensions——the top stem protrudes through the body for handle or actuator mounting, and the bottom trunnion pin passes through the body shell to a bottom bearing plate on the outside. Two external penetrations, two stem seal locations, two potential fugitive emission points. That’s the standard design, and it works. But it carries a structural trade-off that shows up most clearly in two places: ISO 15848 low-emission compliance testing, and long-term seat seal integrity under sustained high-pressure cycling.

FLOWKS support plate type trunnion mounted ball valve eliminates the bottom external penetration entirely. Instead of a bottom trunnion pin passing through the valve body, a lower support plate is integrated into the body cavity itself——the plate sits inside the valve, directly supporting the ball’s lower journal bearing. No shaft penetrates the body shell at the bottom. No external seal, no packing gland, no potential weep path at that location. The upper support plate works the same way: it carries the ball’s upper bearing load inside the body rather than relying on an external sleeve insert pressed into the ball from outside. Two internal support plates handle the full media thrust load——and that’s where the “stronger support” claim comes from. The plates distribute thrust force across a broader contact area than a single shaft journal could, which means less localized stress on the bearing surfaces and more structural rigidity under differential pressure loading at Class 1500 and Class 2500.

Size range is 2" through 48", pressure ratings from Class 150 to Class 2500——same coverage as our standard trunnion mounted forged steel ball valve series. Forged body construction applies here as well. The forged body gives you the material density advantage for high-pressure containment, and the internal support plate design complements it by keeping the pressure boundary cleaner. Fewer external penetrations in a forged body means fewer locations where the continuous pressure envelope gets interrupted by a shaft bore and a packing arrangement. Think of it this way: a forged body shell is a closed pressure vessel. Every shaft bore that passes through it opens a hole in that vessel that has to be re-sealed with packing. The support plate design closes one of those holes permanently. That’s not an incremental improvement——it’s a fundamental structural upgrade.

The sealing principle remains trunnion based. Spring-loaded seats press independently against the anchored ball surface from upstream and downstream directions, creating bidirectional sealing. The ball doesn’t float, doesn’t shift under line pressure——it stays centered and the seats do the sealing work. Seat material options include PTFE for general service, reinforced PEEK for elevated temperature and mechanical strength requirements, Nylon and Delrin (POM) for cost-effective non-aggressive media applications, and PCTFE for low-temperature duty. Once line pressure reaches normal operating range, the valve automatically reinforces sealing——spring preload combined with media pressure drives each seat tighter against the ball.

The fugitive emission advantage deserves a closer look. ISO 15848 compliance testing measures stem seal leakage rates——and every external shaft penetration is a test point. A conventional trunnion ball valve with top and bottom external stems has two independent seal locations that both need to pass. The support plate design removes the bottom penetration, which means one fewer test location, one fewer seal that can degrade over time, and one fewer potential leak path that your emission monitoring system has to track. In practice, that structural simplification translates into more consistent ISO 15848 test results over the valve’s service life. Maintenance teams also benefit——one fewer packing gland to inspect, adjust, and eventually repack during scheduled turnaround work.

Body materials: A216 WCB carbon steel for standard process lines, A351 CF8M austenitic stainless steel for corrosive and chloride-containing media, A182 F51 duplex stainless where corrosion resistance and higher mechanical strength are both required, and A182 F53 super duplex for the most aggressive high-chloride, high-stress environments. The material logic is the same as across the full FLOWKS trunnion series——match the body alloy to what the process and the environment will demand over the intended service interval.

API 6D, API 607, and ISO 15848 certification apply to this series. API 6D covers design, production, and full-pressure testing——shell integrity, seat sealing verification, and operational cycling endurance. API 607 certifies fire-safe performance through burn exposure and post-fire sealing capability. ISO 15848 governs fugitive emission rates for volatile and hazardous media——and here the support plate design gives you a structural head start that conventional trunnion valves don’t have. Fewer external penetrations, fewer seal locations, lower inherent emission risk. The certification proves the valve meets the standard. The design reduces the number of locations that have to prove it.