What Is a Floating Ball Valve?

A floating ball valve is a type of quarter-turn valve in which the ball is not physically fixed by a stem or shaft at both ends. Instead, it “floats” within the valve body, held in place only by the pressure of the valve seats.

This allows the ball to move slightly downstream under the pressure of the fluid, pressing against the downstream seat to create a tight seal.

Key features include:

Two-piece or three-piece construction

A hollow ball with a through-hole (bore)

A single top-mounted stem that rotates the ball

Sealing achieved through ball movement, not seat movement

This floating design works particularly well in low to medium pressure systems where bi-directional sealing is required without the added complexity or cost of a trunnion assembly.

How Floating Ball Valves Work

The key to a floating ball valve’s operation lies in its pressure-activated sealing mechanism. Unlike trunnion-mounted valves, where the ball remains fixed and the seat moves to create a seal, a floating ball valve relies on ball displacement to seal off the flow.

Here’s how it works step by step:

Operating Principle

Fluid enters the valve body under pressure

The pressure causes the ball—held loosely between two seats—to move slightly downstream

This movement pushes the ball tightly against the downstream seat

The resulting compression creates a seal that prevents leakage

This method enables a reliable shutoff, even with relatively simple construction and a single stem.

Bi-directional Sealing (with Limits)

Most floating ball valves offer bi-directional sealing, meaning they can block flow from either direction. However, the sealing quality is typically better in the direction of pressure due to the downstream movement of the ball.

Some designs include secondary sealing aids, like:

Spring-loaded seats to enhance contact

Soft or elastomeric seat materials for better adaptability

Anti-static devices for gas applications

Torque Consideration

Because the ball shifts during operation, floating ball valves usually require more torque to operate than trunnion valves—especially under high pressure.

This is important when selecting actuators or manual operation strategies, particularly in:

Automated valve systems

High-pressure fluid lines

High-viscosity applications

Summary

A floating ball valve seals by allowing the ball to move downstream and press into the seat—simple, effective, and compact for many common industrial uses.

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