Floating Ball Valve: Structure and Sealing Performance

In industrial piping systems, valves are indispensable key components responsible for controlling fluid flow and ensuring the safe and efficient operation of the system. Among various types of valves, the floating ball valve has gained widespread favor across numerous industries due to its unique structure and superior sealing performance. This article delves into the structural characteristics, sealing principles, and application advantages of floating ball valves, as well as considerations for their use, to provide readers with a comprehensive understanding of this efficient and reliable valve solution.

The core component of a floating ball valve is a ball with a through-hole, the diameter of which is equal to the pipe bore. The ball is housed within a metal valve body, with a polytetrafluoroethylene (PTFE) - made sealing seat at both the inlet and outlet ends. When the through-hole of the ball aligns with the pipe passage, the valve is in the open position; when the through-hole is perpendicular to the pipe passage, the valve is closed. The transition from open to closed, or vice versa, requires only a 90-degree rotation of the ball. This simple structural design not only makes the operation of the floating ball valve extremely convenient but also lays the foundation for its efficient sealing function.

Sealing seats are one of the core components for achieving the sealing function in floating ball valves. Typically made from elastic materials such as PTFE, these seats are widely used in sealing applications due to their excellent chemical stability and temperature resistance. In a floating ball valve, the sealing seat and the ball form a sealing pair, creating what is known as a soft-seal structure. The advantage of soft-sealing lies in its ease of ensuring tightness and relatively low requirements for the machining accuracy and surface roughness of the sealing surfaces. This means that in actual production, manufacturing costs can be effectively controlled while ensuring good sealing performance under various operating conditions.

To further enhance sealing performance and extend the service life of the valve, the sealing seats in floating ball valves feature a special elastic structure design. This design includes a 40°±1 angle on the sealing face, an R2 semicircular groove at the bottom of the sealing seat, and a clearance δ1 when assembled with the valve body. These structural features ensure that, without pre-tightening force, the ball is tangent to the sealing seat at point A. When pre-tightening force is applied, the ball shaft will displace, typically by 0.2 to 0.4 millimeters. Under working conditions, when the ball is subjected to pressure, it will tightly adhere to the sealing face, causing the sealing ring to expand outward, thus preventing excessive tightness between the sealing face and the ball surface that could lead to increased torque. After depressurization, the sealing seat can essentially return to its initial position. This elastic structure design not only effectively reduces the frictional torque between the ball and the sealing seat but also enhances the service life and operational reliability of the sealing seat.

The sealing principle of floating ball valves is primarily based on a combination of medium pressure self-sealing and pre-tightening sealing. This method is fundamentally different from traditional forced-sealing valves, such as globe valves and gate valves, which rely on externally applied force for sealing. The latter approach has a certain degree of randomness and uncertainty, which is not conducive to the long-term stable operation of the valve. In contrast, the sealing force of a floating ball valve is generated by the medium pressure, which is stable and controllable, determined at the design stage.

When a floating ball valve is in the closed position, the medium pressure at the inlet end acts on the ball, exerting a force that pushes the ball against the sealing seat at the outlet end. On the conical surface of the sealing seat, this force creates a contact stress, forming a contact band. The force per unit area on the contact band is referred to as the working contact pressure q of the valve seal. When the working contact pressure q exceeds the required contact pressure for sealing, the valve achieves effective sealing. This type of sealing, generated by medium pressure, is called medium self-sealing. The advantage of medium self-sealing is that as the medium pressure increases, the sealing effect correspondingly enhances, ensuring reliable sealing performance even under high-pressure conditions.

Although medium self-sealing plays a crucial role in floating ball valves, under low-pressure conditions, the medium pressure alone may not be sufficient to ensure sealing performance. Therefore, in addition to self-sealing, a certain amount of pre-tightening force is necessary. This pre-tightening force is mainly achieved through the elasticity of the sealing seat itself. During valve assembly, the ball must be in tight contact with the sealing seat, with a certain amount of interference to generate a pre-tightening contact pressure. This pre-tightening contact pressure is typically 0.1 times the working pressure and not less than 2MPa. The achievement of pre-tightening contact pressure entirely depends on the geometric dimensions of the design to ensure it. If the free height of the ball combined with the inlet and outlet sealing seats is A, and the width of the cavity in the combined left and right valve bodies accommodating the ball and sealing seats is B, then the interference C required to generate the necessary pre-tightening contact pressure after assembly must satisfy A-B=C. The size of the interference value C directly determines the sealing performance and operating torque of the valve. Therefore, during the design and manufacturing process, geometric dimensions must be strictly controlled to ensure the accurate realization of the pre-tightening contact pressure.

Polytetrafluoroethylene (PTFE) is the primary material for the sealing seats of floating ball valves. This material is widely used in sealing applications due to its excellent chemical stability and temperature resistance. PTFE's chemical stability is so remarkable that it even surpasses that of precious metals like gold and platinum, as well as glass, ceramics, enamel, special steels, and alloys. Neither concentrated acids, dilute acids, concentrated alkali solutions, nor the strongest oxidizing agents can exert any chemical effect on PTFE. Known as the "King of Plastics," PTFE performs exceptionally well in environments with strong chemical corrosivity. Apart from certain halogenated amines or aromatic hydrocarbons that may cause slight swelling of PTFE, ketones, acids, esters, and other organic solvents have no effect on it, resulting in no weight change or swelling. Additionally, PTFE is unaffected by oxygen or ultraviolet light, is non-hygroscopic, and is non-flammable. It has high heat and cold resistance, with a usable temperature range of -180°C to 250°C. After being treated at 250°C for 240 hours, its mechanical properties remain unchanged; at 390°C, its hourly weight loss is merely 0.006%. PTFE also has excellent dielectric properties, with electrical performance unaffected by frequency and temperature, allowing it to operate long-term at 250°C. These superior properties make PTFE an ideal material for the sealing seats of floating ball valves.

However, PTFE has a relatively high elastic modulus, which means its elastic deformation is limited. Over long-term use, the material's elasticity may not be sufficient to compensate for wear on the sealing surfaces, leading to a decline in sealing performance. To address this issue, the sealing seats of floating ball valves employ an elastic structure design, which enhances the structure's elasticity to make up for the material's insufficiency. This design not only extends the service life of the sealing seat but also ensures the valve's sealing reliability over extended periods of use.

With its unique structure and sealing principles, the floating ball valve demonstrates significant application advantages across various industrial fields.

Floating ball valves are bidirectional sealing valves, meaning they can achieve sealing in both directions of fluid flow. This bidirectional sealing capability endows floating ball valves with great flexibility and reliability in complex piping systems. Regardless of the direction of fluid flow, the valve can effectively prevent medium leakage, ensuring the safe operation of the system. This bidirectional sealing ability is particularly important in piping systems that require bidirectional control, such as in the pipeline transportation of oil, natural gas, and chemicals. Floating ball valves can effectively prevent the backflow of media, avoiding potential safety hazards.

The operation of floating ball valves is extremely simple, requiring only a 90-degree rotation of the ball to switch from open to closed or vice versa. This straightforward operation not only enhances work efficiency but also reduces the labor intensity of operators. Moreover, due to the relatively simple structure of floating ball valves, their maintenance costs are relatively low. Under normal operating conditions, the service life of key components such as the sealing seats and the ball is long, reducing the frequency of component replacement. Even when maintenance is required, the simple structure allows maintenance personnel to quickly identify and rectify issues, thereby minimizing downtime and increasing equipment utilization.

Floating ball valves can adapt to a variety of working media and conditions. Thanks to the use of high-performance materials like PTFE for their sealing seats, which possess excellent chemical stability and temperature resistance, floating ball valves can handle various media with strong chemical corrosivity and both high and low-temperature environments. Whether dealing with acidic, alkaline, or neutral media, floating ball valves can maintain good sealing performance. Additionally, the sealing principle of floating ball valves, which combines medium pressure self-sealing and pre-tightening sealing, ensures reliable sealing under different pressure conditions. Whether under low or high pressure, floating ball valves can operate stably, ensuring the safety and stability of the system.

With its simple structure, reliable sealing performance, and easy operation, the floating ball valve has found widespread application in industrial piping systems. Its unique sealing principles and material selection enable it to maintain stable sealing performance under various complex conditions, meeting the demands of different industries. However, during use, attention should be paid to issues such as static electricity, valve cavity liquid accumulation, and assembly precision to ensure the long-term stable operation of the valve. As technology continues to advance, the design and manufacturing of floating ball valves will become more refined, and their performance will continue to improve, providing a more reliable guarantee for the safety and efficiency of industrial production.