What Are The Structure And Working Principle Characteristics Of Lined Ball Valve?

1. Overview
Commonly used Lined Ball Valve include fixed and floating ball valves. Ball valves are widely used in the petroleum, chemical, power plant, and long-distance oil and gas pipelines due to their low flow resistance, fast opening and closing speeds, and simple operation. The ball valve seal is achieved by combining a pre-set preload between the ball and the valve seat with the force exerted by fluid pressure on the seat sealing surface. This preload is typically achieved by inserting elastic elements, such as disc springs and cylindrical springs, between the seat and the body. During the opening and closing process of a hard-seal ball valve, the preload constantly acts on the sealing surface, resulting in a greater opening and closing torque than other valve types. This preload also increases seal wear, shortening the lifespan of the ball valve. To overcome these shortcomings, a helical drive mechanism is designed between the ball and the valve seat.
A ball valve consists of a valve body, bonnet, ball, valve seat, and valve stem (Figure 1).

A helical drive mechanism is used to move the valve seat along its axis within the valve body. Specifically, a circular drive plate with a helical groove is mounted above and below the ball, rotating with the ball. Drive pins are located above and below the valve seat, engaging with the helical grooves on the drive plate. When the valve is opened or closed, the ball rotates, driving the drive plate with it. When the valve is closed, the helical groove on the drive plate, via the drive pin on the valve seat, pulls the valve seat toward the ball. At the moment of closing, the helical groove, via the drive pin on the valve seat, creates a tight seal with the ball. At the moment of opening, the helical groove, via the drive pin on the valve seat, pushes the valve seat away from the ball, achieving frictionless operation. According to the calculation formula of the valve stem torque of the fixed ball valve, MF = MQC + MFT + MZC (1) Where MF is the valve stem torque of the ball valve, N·mm MQC is the friction torque between the ball and the valve seat sealing surface of the fixed ball valve, N·mm MFT is the friction torque between the packing and the valve stem, N·mm MZC is the friction torque generated by the bearing, N·mm What are the characteristics of the structure and working principle of the hard-sealed ball valve? Since the valve seat moves along the axis by a spiral transmission mechanism, there is no force between the valve seat and the ball during the opening and closing process of the valve, so formula (1) is simplified to MF = MFT + MZC (2) From the calculation of formula (2), it can be concluded that the valve stem torque is greatly reduced. 3. Design of spiral transmission mechanism There are two transmission pins on the upper and lower parts of the valve seat, which are engaged with the four spiral grooves on the transmission disk. The pitch of the spiral groove is 1mm. The helical groove's position begins at the position of the drive pin on the valve seat when the valve is open, and ends at the position of a 90° counterclockwise rotation (Figure 2). The drive disc is connected to the valve stem via a key and rotates with the ball. When the valve is opened or closed, the ball and drive disc rotate, transmitting power to the valve seat through the helical grooves on the drive disc, causing the valve seat to reciprocate along its axis.
4. Conclusion
Compared to existing technologies, this hard-seal ball valve features a compact and simple structure, small size, and lightweight design. This structure also provides bidirectional sealing, fire protection, and anti-static properties. Most importantly, it achieves virtually friction-free operation between the ball and valve seat, extending the valve's service life and reducing the valve's opening and closing torque. This structure is particularly suitable for large-diameter electric ball valves, achieving significant energy savings.