Floating Ball Valve Vs Trunnion Mounted Ball Valve

When selecting the right ball valve for industrial applications, understanding the difference between floating ball valves and trunnion mounted ball valves is crucial. Both types serve the same basic function—controlling the flow of liquids or gases—but their internal structures and performance characteristics vary significantly. In this article, we’ll break down the working principles, structural features, and suitable applications of each type to help you choose the best valve for your needs.

1. Structure and Working Principle of Floating Ball Valves

A floating ball valve features a ball that is not fixed to the valve stem or body, allowing it to "float" slightly within the valve cavity. It is clamped between two seat rings at the valve’s inlet and outlet.

When the valve is in operation, turning the valve stem rotates the ball 90°, opening or closing the flow. Under pressure, the ball moves slightly downstream (toward the outlet), pressing firmly against the downstream seat. This movement creates a tight seal, which is why this design is called a "floating" ball valve.

To ensure a reliable seal, the valve seats are preloaded to grip the ball. As media pressure increases, the ball is pushed more tightly against the outlet seat, improving the sealing performance. However, since the ball is held in place only by the stem and fluid pressure, the seat must bear the ball’s weight and media pressure—especially at larger sizes and higher pressures. Overloading can cause the seat material to deform or fail, resulting in internal leakage.

Common seat materials for floating ball valves include:

• PTFE (Teflon)

• PPL (Polyphenylene)

• Nylon

• PEEK

• Metal (for high-temp or high-pressure service)

2. Structure and Working Principle of Trunnion Mounted (Fixed) Ball Valves

A trunnion mounted ball valve, also known as a fixed ball valve, has a ball supported by both an upper and lower trunnion (stem), which prevents it from moving downstream. The ball remains fixed and rotates in place, driven by the valve stem.

Instead of the ball shifting to seal against a seat, the valve seats are spring-loaded to move toward the ball, creating the seal. This structure allows for consistent and reliable sealing, especially under high pressure. If the seat wears out over time, the spring ensures automatic compensation, maintaining a tight seal.

Since the force from the fluid is applied to a smaller seat surface (rather than the full ball), the torque required to operate the valve is significantly lower than that of a floating ball valve. This makes trunnion mounted ball valves ideal for high-pressure, large-diameter pipelines, such as natural gas transportation (e.g., West-East Gas Pipeline in China with DN1500 and pressure class 1500LB).

Advanced trunnion designs may include:

• DBB (Double Block and Bleed): Seats with single piston effect that can block pressure from both ends and allow cavity pressure relief for safety.

• DIB-I (Double Isolation and Bleed Type I): Seats with double piston effect on both sides, offering tight sealing regardless of pressure from upstream, downstream, or body cavity.

• DIB-II: One seat with single piston effect and one with double piston effect, balancing safety and cost.

Additionally, trunnion ball valves often feature injection ports for emergency sealant to temporarily enhance sealing and extend service life during leaks or maintenance delays.

3. Key Differences Between Floating and Trunnion Mounted Ball Valves

4. Which Type Should You Choose?

Choosing between a floating or trunnion mounted ball valve depends primarily on pressure, media, and valve size:

• For low-pressure systems and small bore pipelines (typically DN50 and below), floating ball valves are more economical and sufficient.

• For high-pressure applications, large pipelines, or where bidirectional sealing and safety features are essential, trunnion mounted ball valves are the best option.

5. Choose Reliable Valve Solutions From a Trusted Manufacturer

At FLOWX, we specialize in manufacturing high-performance floating and trunnion ball valves for a wide range of industries, including oil & gas, chemical, water treatment, and energy.

Our valves are:

• Engineered for long service life

• Certified to international standards (API, ISO, CE)

• Customizable with soft or metal seats

• Available with DBB, DIB, and cavity pressure relief options

If you're looking for reliable, durable, and efficient ball valves, our engineering team is ready to support your projects from consultation to delivery.

Contact us today to get a quote or technical consultation.