According to the sealing materials of the ball valve (the sealing surface of the valve seat and the sealing surface of the ball), it can be divided into two types: soft-seated ball valve and metal-seated ball valve. Soft-seated ball valve means that the sealing surface of the valve seat is made of non-metallic materials, such as PTFE, RPTFE, Nylon, Devlon and PEEK etc. Metal-seated ball valve means that the sealing surfaces of the valve seat and the ball are both made of metal materials, such as Stellite Alloy, chromium carbide, tungsten carbide, Ni60, etc.

In comparison, the soft-seated ball valve has the advantages of good sealing performance, small friction coefficient, easy operation, and is suitable for low pressure, low temperature, clean and less corrosive media. The disadvantage of soft-seated ball valves is that they have poor resistance to high temperature, high pressure, high speed and strong corrosive media, and are prone to aging, deformation and wear.

The advantages of metal-seated ball valves are strong resistance to high temperature, high pressure, high speed and strong corrosive media, stable structure and long service life. The disadvantages of metal-seated ball valves are that the sealing performance is relatively poor, the friction coefficient is larger, the operating torque is larger, and the processing accuracy and process requirements are higher.

Structural characteristics of metal-seated ball valve

The structure of the metal-seated ball valve is mainly composed of a valve body, a ball, a valve stem, a metal seat and a flexible graphite sealing ring between the valve seat and the valve body. Among them, the surface of the metal seat and the ball has been specially treated to improve the hardness and wear resistance and ensure good sealing performance. The flexible graphite sealing ring plays a compensating role, and can maintain a certain pre-tightening force under temperature changes or medium erosion, achieving two-way sealing. In addition, the metal-seated ball valve is also equipped with spring devices, which keep the valve seat in close contact with the ball under lower pressure. In some special working conditions, a sealing grease injection system can also be designed between the seat and the ball to improve reliability and safety.

Working conditions of metal-seated ball valve

Metal-seated ball valves are suitable for high-temperature and high-pressure water, steam, petroleum, coal, fiber, viscous and corrosive media, and also media containing particles. Generally speaking, metal-seated ball valves can withstand pressures up to 35MPa and temperatures up to 300°C. Metal-seated ball valves have good wear resistance, corrosion resistance, erosion resistance and self-cleaning ability under these working conditions.

Performance comparison between metal-seated ball valves and soft-seated ball valves

Metal-seated ball valves and soft-seated ball valves have their own advantages and disadvantages under different working conditions, and they should be selected comprehensively according to specific conditions. Here are some common comparison factors:

• Sealing performance: The sealing performance of the soft-seated ball valve is better than that of the metal-seated ball valve, especially at low pressure, the soft-seated ball valve can achieve zero leakage. The sealing performance of metal-seated ball valves is affected by factors such as machining accuracy, surface quality, and fit clearance, and the leakage rate can only reach Grade IV or Grade V generally.

• Temperature resistance: Metal-seated ball valves have better temperature resistance. The sealing material of soft-seated ball valves is prone to aging, deformation and ablation at high temperatures, while the temperature resistance of metal-seated ball valves can generally reach up to 300°C, mainly depending on the choice of metal materials and flexible graphite.

• Pressure resistance: Metal-seated ball valves have better pressure-resistant performance. The sealing material of soft-seated ball valves is easy to squeeze out, crack and fail under high pressure, while the pressure resistance of metal-seated ball valves can generally reach up to 35MPa, mainly depending on the choice of metal materials and structural design.

• Wear resistance: Metal-seated ball valves have better wear resistance, especially in media with particles or high-speed flow, and the sealing material of soft-seated ball valves is easy to wear, scratch and fall off. The wear resistance of the metal-seated ball valve mainly depends on the choice of metal material and surface treatment. The hardness of the sealing surface can reach HRC72.

• Operability: Soft-seated ball valves have better operability, especially in the case of low temperature or low friction coefficient. The operating torque of soft-seated ball valves is small and easy to operate. The operating performance of the metal-seated ball valve is affected by the metal material and friction coefficient, and generally requires a large operating torque or is equipped with a transmission device.

• Maintenance performance: Soft-seated ball valves are easier to maintain. The valve seat of the soft-seated ball valve is easy to replace and the cost is low. The maintenance of metal-seated ball valves is affected by metal materials and machining accuracy, and generally requires professional equipment and technology for replacement or repair.

Summarize

Metal-seated ball valve is a ball valve suitable for high temperature and high pressure, strong corrosion and medium with particles. It has the advantages of stable structure, long service life, wear resistance and corrosion resistance. Compared with soft-seated ball valves, metal-seated ball valves have different performance advantages and disadvantages under different working conditions, so comprehensive consideration should be made according to specific conditions when selecting.