The eccentric half-ball valve and the fixed ball valve have significant differences in terms of structural design, sealing performance, application scenarios, and operational characteristics. The following is a detailed comparative analysis of the two: 

I. Structural Design 

1. Eccentric Hemisphere Valve: 

The eccentric half-ball valve adopts an eccentric design, with an eccentricity between the valve shaft and the centerline of the hemisphere. This design ensures that the contact between the ball core and the valve seat only occurs at the moments of valve closure and opening, thereby reducing the wear on the valve core and valve seat. 

The spherical surface of the eccentric half-ball valve usually does not have a V-shaped opening. Its sealing surface design focuses on achieving a tight cut-off. 

2. Fixed ball valve: 

The ball body of the fixed ball valve is supported and fixed by the upper and lower valve stems. It can only rotate and cannot move horizontally. It usually has a floating valve seat. When subjected to the pressure of the medium, the valve seat moves, causing the sealing ring to tightly press against the ball body to ensure sealing. 

The ball structure of the fixed ball valve is relatively simple, but it has stable and reliable sealing performance and is suitable for high-pressure and large-diameter applications. 

II. Sealing Performance 

1. Eccentric Hemisphere Valve: 

The eccentric half-ball valve has excellent sealing performance, especially in situations requiring precise isolation. Its eccentric design enables the ball core to closely fit the valve seat when closed, achieving zero leakage. 

The eccentric half-ball valve also has a self-cleaning function. When the ball is detached from the valve seat, the fluid in the pipeline passes uniformly along the sealing surface of the ball in a 360° circle, flushing away the accumulated substances on the sealing surface and helping to maintain the cleanliness and sealing performance of the sealing surface. 

2. Fixed ball valve: 

The sealing performance of the fixed ball valve is also reliable. Its floating valve seat design can adapt to changes in medium pressure, maintaining a tight fit between the sealing ring and the ball. 

Fixed ball valves usually have a two-way sealing function. That is, regardless of whether the valve is fully open or fully closed, the valve seats on both the upstream and downstream sides can block the flow of fluid, thereby enhancing the safety and reliability of the valve. 

III. Application Scenarios 

1. Eccentric Hemisphere Valve: 

The eccentric half-ball valve is widely used in industries such as petroleum, chemical engineering, and urban water supply and drainage where precise isolation is required. Its unique eccentric design and self-cleaning function enable it to perform exceptionally well when dealing with media containing fibers, particles, and other impurities. 

The eccentric half-ball valve is also applicable in scenarios such as sewage treatment, pulp processing, alumina production, urban heating and cooling, as well as in power plants, water removal from slag in hydropower, or gas transmission pipelines. 

2. Fixed ball valve: 

Fixed ball valves are suitable for long-distance pipelines and general industrial pipelines, especially in high-pressure and large-diameter applications. Their strength, safety, and resistance to harsh environments have been specially considered during design, and they are applicable to various corrosive and non-corrosive media. 

Fixed ball valves are also widely used in fields such as petroleum refining, chemical industry, papermaking, pharmaceuticals, water conservancy, power, municipal services, and steel production. 

IV. Operational Characteristics 

1. Eccentric Hemisphere Valve: 

The eccentric half-ball valve has a small opening and closing torque and is easy to operate. Its eccentric design reduces the friction between the ball core and the valve seat during rotation, thereby lowering the operational difficulty and energy consumption. 

The eccentric half-ball valve also has a cutting function. When closed, it can cut off the impurities in the medium, ensuring the normal opening and closing of the valve. 

2. Fixed ball valve: 

The operation of the fixed ball valve is also effortless. The ball is supported by upper and lower bearings, reducing friction and torque. 

Fixed ball valves are usually equipped with advanced actuators and control devices, enabling remote control and automated operation.