Trunnion-mounted ball valves use a fixed ball design to manage high pressure in large pipelines. Their body structure determines how the valve is assembled and maintained. The two-piece and three-piece body configurations are the most commonly used in industrial projects.
In this guide, we will explore the differences between the 2-piece trunnion ball valve vs 3 piece trunnion ball valve. We will highlight their pros and cons, maintenance practices, and selection criteria for oil and gas pipeline projects.
2 Piece Trunnion Ball Valves: Pros and Cons
A 2-piece ball valve has two body sections joined by threads or flanges and is widely used for controlling liquid and gas flow. One section forms the body and end connection, while the other holds the trim and outlet, enabling bidirectional shutoff or full-port service.
Pros
- Easy Installation: They are lightweight and have a small diameter, making it easy to install. Its small actuator size also facilitates frictionless movement.
- Minimal Fluid Resistance: Its resistance coefficient is similar to that of an equal-length pipe, allowing fluids to flow through seamlessly.
- Good Sealing: These valves close tightly and have a strong seal, reducing leakage possibilities. Materials like metal, EPDM, EPR, and PTFE are commonly used on the sealing surface.
- Operational Convenience: They can be easily opened and closed as desired when rotated to a complete right angle. Moreover, it can be remotely operated if needed.
- Easy Maintenance: The valve’s structure is simple, making it easy to maintain. When it is fully open or closed, the seat sealing surface is isolated from fluid that helps minimize the risk of the sealant’s erosion.
Cons
- Not ideal for throttling.
- Wear in dirty fluids.
- Size limitations in high-pressure systems.
- Higher initial costs.
3 Piece Trunnion Ball Valves: Pros and Cons
A 3-piece ball valve comprises three pieces, particularly, a pair of connecting ends and the main body. The end cap can be connected to the pipeline through a flanged, clamped, welded, or threaded assembly. Engineers often choose this version for large-bore flanged ball valves in heavy-duty environments.
Pros
- Sound Design: These valves can be easily assembled and disassembled thanks to their three-piece, simple, and lightweight design.
- Low Fluid Resistance: Their resistance coefficient is equal to the pipe diameter of the same length for 3-piece ball valves. This allows smooth flow and reduces blockage risk. Most 3-piece ball valves also use full-bore designs for higher flow capacity.
- High Sealing Performance: These valves make changing seals and seats more affordable. It also creates a strong seal that prevents leaks as they close tightly when welded.
- Operational Ease: These valves are ideal for frequent and rapid opening and closing, by turning the lever to 90 degrees, without friction. They also facilitate remote operation if needed.
- Easy Maintenance: They enable easy maintenance, as the central body can be removed without detaching end caps or pipe connections, allowing the line to operate during servicing. The body can also be handled and welded separately, protecting the internal components from damage.
Cons
- The highest initial cost compared to other types.
- Bulkier and more complex constructions.
Selection Criteria for Oil & Gas Pipeline Projects
Selection requires assessing the total cost of ownership, flange requirements, and weight limits for your piping supports.
2-piece valves are more affordable for initial purchase in smaller sizes. They also provide a compact footprint for tight installation spaces in pumping stations. Meanwhile, 3-piece valves are better for projects needing frequent seat replacements.
Moreover, consider the media being transported through the pipeline, like abrasive fluids that cause faster wear on internal components. Ultimately, ensure the trunnion ball valve manufacturer provides full material traceability for all body parts. Following these steps ensures the valve survives the harsh conditions of oil and gas transport.
Conclusion
Choosing between two-piece and three-piece trunnion valves depends on maintenance needs and leak risks. The former one offers a simpler body with fewer seals for high-pressure safety, while the latter provides superior access for in-line repairs and long-term serviceability.
Onero Valve has a wide range of trunnion ball valves suitable for high-pressure applications (2″–48″, 150–2500 LB), handling water, gas, oil, and corrosive media from −196 °C to 350 °C. It also ensures tight sealing, meeting API 6D and ASME standards, with manual, pneumatic, or motorized operation.
