--- title: "Trunnion Ball Valve: Design Engineering & Selection Guide" date: 2026-08-04T09:42:00Z modified: 2026-08-26T00:48:06Z permalink: "https://www.tgvalve.com/blog/trunnion-ball-valve/trunnion-ball-valve-design-and-engineering-guide/" type: post status: publish excerpt: "" wpid: 3004 categories: - Trunnion Ball Valve featured_image: "https://www.tgvalve.com/wp-content/uploads/2026/08/image-86.webp" featured_image_alt: An industrial worker operating a blue handwheel on a heavy-duty trunnion ball valve integrated into a complex high-pressure pipeline network at an oil and gas facility timestamp: 2026-08-26T00:48:06Z tags: - Trunnion Ball Valve --- ## Quick Answer: Trunnion Ball Valves for High-Pressure Flow Control. A trunnion ball valve locks the ball on top and bottom anchors, keeping heavy pressure off the seats. This fixed design reduces operating torque and ensures precise sealing in high-pressure, large-bore pipelines. TG Valve builds API 6D and ASME B16.34 valves, backed by mill certs and torque test data for global engineers. This guide discusses the trunnion ball valve which is a quarter-turn, shut-off valve designed for high-pressure, large diameter pipelines. The [trunnion ball valve selection](https://www.tgvalve.com/wp-content/uploads/wp-mfa-exports/page/industrial-ball-valve-manufacturer-supplier.md) process requires matching the service conditions to the right design that meets the applicable API/ ISO standards. Choosing the right trunnion valve also factors materials, bore, end connections, and actuation. [TG Valve](https://www.tgvalve.com/wp-content/uploads/wp-mfa-exports/page/sample-page.md) manufactures these valves which meet API 6D and ASME B16.34 requirements for pipeline and processing clients globally. The company also supports each order with API 6D certification, full mill test reports, and a track record across 40+ global markets. ## What Is a Trunnion Mounted Ball Valve and What Are Its Components? ![A diagram of a trunnion ball valve design components and how each works](https://www.tgvalve.com/wp-content/uploads/2026/08/image-87.webp) A trunnion ball valve holds the ball in a fixed position using pins at the top and bottom, independent of the seats. It is also known as a fixed ball valve or a trunnion type ball valve. It has seven components that work together in providing sealing and control. 1. **Body:** Houses the ball, seats, and internal cavity. It comes in forged, cast, or welded construction depending on pressure and size. 2. **Ball:** This component is a solid or hollow sphere with a bored passage that rotates a quarter turn to open or close the flow path. 3. **Trunnion pins:** These parts extend from the top and bottom of the ball into bushings in the body. They anchor the ball on a fixed axis. 4. **Bearings:** They sit between the trunnion pins and body. They cut friction during rotation. 5. **Stem:** This part connects the actuator or handwheel to the ball. It transmits rotation without carrying the ball’s weight. Many designs use an anti-blowout stem that stays captured inside the body even if the packing fails. 6. **Spring-loaded seats:** These seats sit on each side of the ball and use spring force to hold contact and seal against line pressure. 7. **Seals:** These include O-rings and gaskets. They close the gaps at the stem, body joints, and seat pockets to prevent external leakage. ## What is the Trunnion Valve Working Principle? ![A diagram showing the trunnion ball valve working principle](https://www.tgvalve.com/wp-content/uploads/2026/08/image-88.webp) The trunnion ball valve working principle relies on seat movement rather than ball movement. It has spring-loaded seats that push toward the fixed ball to create a tight seal on both sides. Springs drive that seal, so it holds tight even at low or no pressure. On the other hand, a floating ball valve works differently. In this design, the ball itself shifts toward the downstream seat under line pressure. Comparing the trunnion vs floating ball valve, the trunnion design carries pipeline loads through the pins, not through the seats. This structural difference matters most at large diameters and high pressure classes. Like most ball valves, they are designed for fully open or fully closed services, not for throttling. ## How Does Seat Design Affect Trunnion Valve Performance? Seat design determines whether a trunnion type ball valve seals in one direction or both directions equally. There are two seat designs to consider: single piston effect (SPE/uni-directional) and double piston effect (DPE/ bi-directional). Single piston effect seats, or SPE, release upstream cavity pressure and require a relief mechanism to prevent over-pressure build-up. It has built-in body vents and drains at the top and bottom to release trapped gas or fluid from the valve cavity. A double piston effect, or DPE, traps cavity pressure and requires a relief mechanism to prevent over-pressure buildup. ### What are the Differences Between SPE / DPE Seat Design? The main differences between SPE / DPE seat design are based on line conditions, cavity relief needs, and client specifications. It presents two configurations: double block and bleed or DBB, and double isolation and bleed or DIB. In a [double block and bleed](https://www.tgvalve.com/wp-content/uploads/wp-mfa-exports/post/what-is-a-double-block-bleed-valve.md) (DBB) configuration, it has a single valve with two seating surfaces that seals against pressure from both ends when closed. Its means of venting/ bleeding the cavity is between the seating surfaces. Meanwhile, the double isolation and bleed (DIB) configuration also has a single valve with two seating surfaces. The difference is that it seals against pressure from a single source. The venting/bleeding process is the same as DBB configuration. ## Why Choose a Trunnion Ball Valve Design for High-Pressure Pipelines? Trunnion valve designs require less operating torque than [floating ball valves](https://www.tgvalve.com/product/high-pressure-forged-floating-ball-valve/), making them ideal for high-pressure, large-bore pipelines. For example, a 24-inch Class 600 valve typically needs about 36,000 N-m to operate. This exceeds the typical floating ball actuator ranges. Seats never carry the ball’s full weight, so actuators can run smaller and are cheaper to install. The trunnion ball valve design suits pressure classes above 1500 psi and pipeline diameters exceeding 24 inches. Large diameter, high-pressure lines depend on this torque advantage to keep actuation practical. It also helps keep maintenance manageable over decades of service. ## Which Standards Apply to API 6D Trunnion Ball Valve Units? There are four standards that apply to [API 6D](https://www.tgvalve.com/wp-content/uploads/wp-mfa-exports/post/what-is-api-6d.md) trunnion ball valve units. These units follow pipeline valve requirements covering design, testing, and marking based on ASME B16.34, API 6FA, API 608, and MR0175. - ASME B16.34 sets pressure-temperature ratings and material limits for the valve body and trim. - API 608 covers metal ball valve design specifically built for on/off pipeline isolation service. - API 6FA fire-safe testing confirms the valve holds pressure through a fire event without catastrophic leakage. - NACE MR0175 governs material selection for sour service, where hydrogen sulfide can crack standard carbon steel. ## How Do You Approach Trunnion Ball Valve Selection? Trunnion ball valve selection starts with matching valve specifications to real line conditions, not just catalog ratings. Five criteria carry the most weight in that decision. 1. **Pressure class:** This sets the wall thickness, seat rating, and body strength needed to hold line pressure safely. 2. **Temperature range:** This determines seat material and seal compound, since extreme heat or cold can harden or crack standard elastomers. 3. **Media:** This determines whether sour gas, crude, or LNG is compatible with trim material and seat to prevent corrosion or seal failure. 4. **Size:** This affects actuator torque requirements and determines whether a forged or cast body is more practical. 5. **End connections:** They must match the pipeline spec to avoid leak paths at the joint. Different connection types are flanged, butt weld, or threaded. Material selection is equally important because the wrong metal can fail under corrosion or thermal stress. - Carbon steel suits standard pipeline service at moderate temperatures and non-corrosive media. - SS316 handles corrosive or higher-purity media streams where carbon steel would degrade over time. - Exotic alloys like Inconel or Duplex steel become necessary in severe service, including sour gas or wide temperature swings. Choosing the right material prevents costly failures and unplanned shutdowns later. ## What Testing Confirms Valve Reliability Before Shipment? Three tests confirm a valve is ready for pipeline service before it ever leaves the factory. - **Hydrostatic testing:** Hydrostatic testing fills the valve with water at 1.5 times its rated working pressure to check shell and seat integrity. - **Pneumatic testing:** Pneumatic testing uses air or inert gas at lower pressure to verify seat sealing without the risk of a liquid burst. - **Fire safe testing:** Fire safe testing per API 6FA exposes the valve to open flame, then confirms it still isolates flow afterward. Pipeline engineers in oil and gas rely on these three tests before accepting delivery, since a valve that fails any one of them risks unplanned downtime in the field. Many procedures also crack the valve open during the shell test for even seat loading. ## Where Do Trunnion Ball Valves Perform Best? Trunnion ball valves perform best in high-pressure, large-diameter applications where floating designs would need oversized actuators. - [**Oil and gas pipelines**](https://www.tgvalve.com/wp-content/uploads/wp-mfa-exports/page/oil-gas-pipeline-valve-solutions.md)**:** Long-distance pipelines use trunnion valves for mainline isolation, since low torque keeps actuation manageable across hundreds of valve stations. - **LNG:** [LNG facilities](https://www.tgvalve.com/wp-content/uploads/wp-mfa-exports/page/lng-cryogenic-valve-solutions.md) specify trunnion designs for cryogenic-adjacent isolation points, where tight shutoff prevents costly product loss during transfer. - **Natural gas transmission:** Natural gas transmission lines depend on bidirectional sealing to isolate segments safely during maintenance or emergency shutdown. - **Subsea:** Subsea systems rely on trunnion valves because the fixed-ball design withstands external pressure and needs less frequent actuator maintenance underwater. Full bore trunnion valves also allow pipeline pigging for cleaning and inspection tools. ## Why Partner With TG Valve on Your Next Trunnion Mounted Ball Valve Project? Choosing a trunnion mounted ball valve requires partnering with a manufacturer who not only shares data specs, but also guarantees field performance. TG Valve manufactures API 6D trunnion ball valve units that engineers can rely on for high-pressure pipelines, LNG terminals, or subsea systems. Hero Product Highlight [ ![API6D Casting Trunnion Ball Valve](https://tgvalve.b-cdn.net/wp-content/uploads/2025/06/Trunnion-Ball-Valve-800x800.jpg) API6D Casting Trunnion Ball Valve **Body and Ball:** Carbon Steel, Stainless Steel, Low-Temperature Carbon Steel, Duplex, Super Duplex, Inconel View Product ](https://www.tgvalve.com/product/api6d-casting-trunnion-ball-valve/)## Frequently Asked Questions ### What is the real difference between a floating ball valve and a fixed-ball design? A floating ball moves against the seat under pressure. A fixed-ball design holds the ball with top and bottom pins, so the seats move instead, lowering operating torque at high pressure. ### Can this valve type handle sour gas service? Yes, when built with materials meeting NACE MR0175. TG Valve selects trim and body materials rated for hydrogen sulfide exposure, so the valve resists cracking in sour service pipelines. ### How often does this valve need maintenance compared to a floating design? Less often. Since the seats, not the ball, carry sealing force, wear spreads more evenly. Lower torque also reduces actuator strain, extending service intervals during continuous pipeline operation. [Get Free Quote](https://www.tgvalve.com/wp-content/uploads/wp-mfa-exports/page/contact.md)