Lined Ball Valve Working Principle And Structure Description

1. Operating Principle: A handle or other actuator applies a torque to the upper end of the valve stem, which is transmitted to the ball, causing it to rotate 90 degrees. The ball's through-hole aligns with or becomes perpendicular to the centerline of the Lined Ball Valve body passageway, completing the opening and closing motion. Clockwise rotation closes, counterclockwise rotation opens.
2. Structural Description: Hard-seal ball valves are designed according to API 6D specifications. They primarily consist of a valve body, seat, ball, stem, and actuator. Two configurations are available: packing seal and O-ring seal.
① For temperatures above 100°C, a packing seal is used. The ball and seat are hard-sealed. Graphite packing is used on the static pressure surface of the seat and the stem. Thrust pads between the stem and gland flange and between the ball and support plate are eliminated. The gland flange and support plate are nitrided. (This configuration is not subject to operating temperature restrictions and can generally be used up to approximately 500°C.) ② For temperatures ≤ 100°C, an O-ring seal is used. The structure is basically the same as that of a conventional fixed ball valve (oil filling device is required at the valve seat and valve stem). O-rings are used to seal the static pressure surface of the valve seat and the valve stem, but hard seals are used between the ball and the valve seat. Pure PTFE thrust pads are used between the valve stem and the gland flange, and between the support plate and the ball. The following is a detailed introduction to the structure of the hard-sealed fixed ball valve with packing seal: (1) Sealing structure: An elastic valve seat is used, and a group of springs are arranged along the circumference of the cross section of the valve channel to always keep the valve seat pressed against the ball to achieve a pre-tightened state. When the fluid pressure of the valve seat is very low, the spring thrust is used; when the fluid pressure is high, the unbalanced force generated by the fluid pressure on the valve seat ensures that the pressure area A1 of the sealing valve seat is greater than the reverse pressure area A2 of the valve seat. The unbalanced force generated by the fluid pressure on the elastic valve seat pushes the valve seat in front of the valve toward the ball, pressing and maintaining the seal. The higher the fluid pressure, the more conducive to the sealing of this structure. (2) Connection form The valve cavity connection adopts flange bolt structure, and the cavity seal is made of graphite sandwiched with stainless steel wire wound gasket. (3) Double blocking and relief function Since the valve seat is sealed before the valve, the two valve seats can independently cut off the fluid at the inlet and outlet ends, thus realizing the double blocking function. When the ball is closed, even if the two ends of the valve are pressurized at the same time, the valve cavity and the two end channels are blocked from each other, and the remaining pressure in the cavity can be discharged through the relief valve (VENT) installed on the valve body. (4) Pressure relief and discharge structure ① When the ball valve is in the closed position, the pressure will be trapped in the cavity of the valve body. When the pressure is too high, it will affect the sealing of the ball valve. Therefore, an NPT pressure relief hole is set as high as possible in the cavity of the valve body and blocked with a relief valve during assembly. ② An NPT screw plug is set at the lowest position of the valve body to discharge dirt. ③ When the valve is ≤4", the pressure relief hole (VENT) and the drain hole (DRAIN) can be combined into one, and a relief valve can be installed at the lowest possible position of the valve. (5) Valve stem anti-blowout function The bottom end of the valve stem is designed with an integral shoulder to prevent the valve stem from blowing out.