Compared to soft sealed ball valves, metal to metal seated ball valves not only have the characteristics of low fluid resistance, quick and convenient opening and closing, good sealing performance, long service life, high reliability, and easy installation with electric and pneumatic devices, but also can adapt to a wider range of temperature and fluid medium fields. Therefore, they are widely used in pipeline transportation. The ball and seat of a hard sealed ball valve are both made of metal materials, and a sealing pair composed of metal and metal materials is commonly referred to as a hard seal. The design specifications for hard sealed ball valves shall comply with API 6D. Mainly composed of valve body, valve seat, sphere, valve stem, and driving device.

For occasions above 100 ℃, use a packing sealing structure. The ball and valve seat are hard sealed. The static pressure surface of the valve seat and the valve stem are sealed with graphite packing. Remove the thrust pads between the valve stem and the gland flange, as well as between the sphere and the support plate. Gland flange and support plate are nitrided. This structure is not limited by the usage temperature and can generally be used up to around 500 ℃;

For situations where the temperature is less than or equal to 100 ℃, use an O-ring sealing structure. The structure of the fixed ball valve is generally the same as that of a conventional fixed ball valve (an oil injection device is required at the valve seat and valve stem). The static pressure surface of the valve seat and the valve stem are both sealed with O-ring seals, except that the ball and valve seat are hard sealed. Pure PTFE thrust pads are used between the valve stem and the gland flange, as well as between the support plate and the sphere.

The sealing structure of the hard sealed fixed ball valve with packing seal adopts an elastic valve seat, and a group of springs are arranged along the circumference of the valve channel cross-section to always maintain the valve seat pressing against the ball and achieving a pre tightened state. When the fluid pressure on the valve seat is very low, it relies on the thrust of the spring; When the fluid pressure is high, the unbalanced force generated by the fluid pressure on the valve seat ensures sealing. The compressed area of the valve seat is greater than the reverse compressed area of the valve seat. The unbalanced force generated by fluid pressure on the elastic valve seat pushes the valve seat forward towards the sphere, compressing and maintaining the seal. The higher the fluid pressure, the more favorable it is for the sealing of this structure.