Firstly, a one-piece ball valve is a manual valve. Its structure is of an integrated type, with the ball being stabilized by a plug head. This design makes maintenance easier and the ball's valve diameter is relatively small. It is inserted from one side of the valve body, and the valve seat needs to be screwed in before pressing down on the ball. Some non-standard one-piece ball valves have a short structure, so the best way to distinguish them is by the structure of the valve body. A one-piece ball valve is fixed by a plug head, which is convenient for maintenance and practical. It is commonly used in small-sized valves. 

The two-piece ball valve is called a stainless steel ball valve. It is composed of two valve bodies connected by bolts on the left and right. When fixed, two valve bodies hold the ball valve in place. However, it is more difficult to maintain. The key point is to check the tightness of the middle screws. This directly affects the tightness of the seal. Additionally, it is mainly used in normal pressure and high-pressure environments. For example, non-standard nominal diameters below DN50 also belong to two-piece valves. The two-piece ball valve fixes the ball with two valve bodies. Maintenance is relatively complex. The tightness of the middle screws is very crucial and directly relates to whether there is leakage. It is a commonly used valve. 

The three-piece ball valve is similar to the two-piece ball valve, but the three-piece type can be used in ultra-high pressure environments. The valve's structure design features three valve bodies, which are fixed by the neck flanges on both sides. The normal nominal diameter is above DN50. The three-piece ball valve is somewhat similar to the two-piece type, but there are multiple valve bodies in the middle of the ball, which are held by the neck flanges on both sides. It is commonly used for larger and more important valves. 

Applicable to: 

Operating temperature: -29 to 180℃ (with reinforced polytetrafluoroethylene sealing ring) or -29 to 300℃ (with isotactic polyphenylene sealing ring). It is used to cut off or connect the medium in the pipeline. 

By choosing different materials, they can be respectively applied to water, steam, oil products, nitric acid, light industry, food, medicine, and environmental protection. They are widely used in various media such as petroleum, chemical industry, metallurgy, electricity, and so on. 

Advantages: 

Ball valves are mainly used in pipelines for cutting, distributing and changing the flow direction of the medium. The ball valve is a new type of valve that has been widely adopted recently. It has the following advantages: 

1. It has low fluid resistance, and its resistance coefficient is equal to that of a pipe section of the same length. 

2. Simple structure, small size, and light weight. 

3. Compact and reliable. The sealing materials used in current ball valves are mostly plastics, which offer excellent sealing performance. They have also been widely adopted in vacuum systems. 

4. The operation is convenient, with quick opening and closing. From fully open to fully closed, it only requires a 90° rotation, making it easy to control from a distance. 

5. Easy to maintain. The ball valve has a simple structure and the sealing rings are usually movable. Therefore, disassembly and replacement are quite convenient. 

6. When fully open or fully closed, the sealing surfaces of the sphere and the valve seat are isolated from the medium. When the medium passes through, it will not cause erosion to the valve sealing surfaces. 

7. Wide application range. The diameter can range from a few millimeters to several meters. It can be used from high vacuum to high pressure. When the ball rotates 90 degrees, at the inlet and outlet, it should present a complete spherical shape, thereby cutting off the flow. 

The ball valve can be closed tightly with a simple 90-degree rotation and a very small torque. The completely equal inner cavity of the valve provides a low-resistance, straight-through flow path for the medium. It is generally believed that the ball valve is most suitable for direct opening and closing applications, but recent developments have made the ball valve capable of having functions of throttling and controlling flow. The main features of the ball valve are its compact structure, ease of operation and maintenance, and suitability for general working media such as water, solvents, acids and natural gas, as well as for media with harsh working conditions such as oxygen, hydrogen peroxide, methane and ethylene. The valve body of the ball valve can be either integral or modular.