Trunnion Mounted Cast Ball Valve

Same trunnion anchored ball, same spring-loaded bidirectional seats——but the body takes shape through a completely different process. A cast steel trunnion mounted ball valve is built by pouring molten metal into precision-engineered molds, and that molding process does something forging simply can’t match at larger sizes: it allows the internal cavity to form with the exact flow contour geometry the design calls for, without the machining constraints that forged bodies face when carving out complex internal passages. In a 36-inch valve, that difference in internal flow path quality isn’t cosmetic——it affects pressure drop, flow coefficient, and how the media moves through the valve bore under real operating conditions.

FLOWKS trunnion mounted cast steel ball valves span sizes from 2" through 48" with pressure ratings from Class 150 to Class 2500. The cast body construction offers a straightforward cost advantage at larger bore sizes——above roughly 12 inches, the forging process becomes increasingly expensive per unit because the material volume and machining complexity scale up sharply, while casting maintains relatively stable unit economics through mold reuse. For projects specifying multiple large-bore valves across a pipeline network, that cost differential compounds quickly. Cast steel isn’t the budget option; it’s the practical option when the spec calls for big valves in quantities that matter to the project bottom line.

Side-entry body design applies here as well. The ball and seat assemblies load through a side opening in the cast body, same principle as the forged series——internals can be accessed without disconnecting the pipeline flanges on both ends, and on welded installations the side-entry access is what makes in-line maintenance possible at all. The cast body actually has a subtle advantage in this configuration: the side-entry cover flange area can be designed with more generous wall thickness and bolt circle geometry during the casting process, because the mold allows shape complexity that would require additional machining passes on a forged body. Thicker cover flanges mean more reliable gasket compression over years of thermal cycling and pressure fluctuations. That detail doesn’t show up in a datasheet, but it shows up in the field.

The trunnion structure solves the same torque and sealing challenges as in the forged version. The ball stays anchored——pinned at top and bottom——and the spring-loaded seats create independent upstream and downstream seals. Bidirectional sealing capability means the valve holds pressure from either direction, which matters in pipeline systems where flow direction can reverse during upset conditions or where double-block isolation is required for safe maintenance access. Because the ball doesn’t shift under media pressure, operating torque stays predictable across the full pressure range. A 24-inch cast trunnion ball valve at Class 600 requires an actuator sized for seat friction alone, not for overcoming line pressure against a floating ball——and that torque predictability carries through to Class 1500 and Class 2500 service where floating designs simply can’t operate at those pressure ratings regardless of body material.

Body materials align with the same critical alloy grades: A216 WCB carbon steel for general process and utility service, A351 CF8M austenitic stainless steel for corrosive environments, A182 F51 duplex and A182 F53 super duplex for high-stress, high-chloride conditions where standard austenitic stainless reaches its limits. The casting process handles CF8M particularly well——austenitic stainless castings have decades of proven service history in petrochemical and offshore applications. F51 and F53 in cast form deliver the same duplex mechanical properties; the casting process has been refined to maintain the required phase balance and microstructure control that gives duplex grades their combination of corrosion resistance and strength.

All valves meet API 6D and API 607 requirements, with ISO 15848 fugitive emission compliance on specified configurations. API 6D certification covers the full design, production, and testing regime——shell integrity, seat sealing under high and low pressure, and operational cycling endurance. API 607 verifies fire-safe performance through burn testing and post-fire sealing verification. ISO 15848 governs stem seal leakage rates for volatile and hazardous media applications. These aren’t checkboxes——they represent the testing evidence that proves the valve performs as rated under the conditions your pipeline will actually experience. Cast or forged, the proof is the same. The body process is what you choose based on your size requirements, quantity economics, and project priorities. The sealing performance, safety certification, and operational reliability——those come standard either way.