Floating ball valves is usually not a two-way seal, its sealing design is directional, but can be achieved through special structure or improvement of bidirectional functions. Here's a breakdown:
1.Seal Direction of Standard Floating ball valves
One-way sealing principle
The sphere of the floating ball valve has no fixed support, and it relies on medium pressure to push the sphere onto outlet valve seat, forming a unilateral forced seal (usually the outlet end). The sealing mechanism is as follows:
High pressure side (inlet): Medium pressure propels the ball to seal the outlet valve seat.
Low pressure side (outlet): If the medium flows in the opposite direction, the outlet side becomes the high pressure side, but due to its own weight or lack of pre-tension, the ball may not fit tightly with inlet valve seat, causing leakage.
Typical application scenarios
Standard floating ball valves are suitable for working conditions in unidirectional flowing media such as:
Water treatment system (unidirectional water supply)
Natural gas transmission (unidirectional air flow)
Acid-base corrosive medium pipeline (unidirectional chemical flow)
In these cases, the flow direction of the medium is fixed and no reverse seal is required.
2. Conditions for two-way sealing of Floating ball valve
Structural improvements
By special design, floating ball valve can be sealed in both directions, provided the following conditions are met:
Double valve seat design: Floating valve seats is arranged on both sides of the sphere, using spring or medium pressure to press the ball at the same time.
Seal surface optimization: use of cemented carbide or high-performance polymer materials to improve valve seat and sphere suitability and abrasion resistance.
Preload adjustment: The two side valve seats are pre-tensioned through springs or mechanical devices to ensure that they remain sealed when low or no intermediate pressure is applied.
Application restrictions
Even if two-way sealing is achieved, the two-way performance of the ball valve is still limited by the following factors:
Pressure balance: When the fluid is inverted, the pressure distribution is not uniform, which may lead to an uneven seal.
Wear accumulation: Long-term two-way opening and closing accelerates valve seat wear and requires more frequent maintenance.
Increased costs: Bidirectional design requires additional components (such as springs and double valve seats) and is more expensive than standard one-way valves.
3. Comparison of bidirectional sealing and Fixed ball valve
Advantages of bidirectional sealing of Fixed ball valve
Fixed-ball valves achieve stable two-way sealing through the following mechanisms:
Sphere fixation: The sphere is supported by the upper and lower stem, and the position is fixed, reducing the risk of surface deviation.
Seat Floating: The two sides of the seat float independently through spring or medium pressure, automatically compensating for wear and tear and maintaining a bidirectional sealing.
Bidirectional preload: regardless of the media direction, the seat can actively press the ball, sealing performance is more reliable.
Selection recommendations
Strict bidirectional sealing: use fixed ball valves, especially for high pressure, large diameter or frequent reverse flow conditions (such as oil refining, long pipeline).
Cost-sensitive and one-way flow: Standard floating ball valves are more cost-effective and meet basic sealing requirements.
Special bi-directional requirements: If a floating ball valve must be used, it must be determined by special design (e.g. double seat, spring spring preload whether the floating ball valve is bidirectional function and a long-term reliability assessment must be made.
