Eccentric hemispherical valves are divided into two structural forms: "side mounted" and "upper mounted", depending on the orientation in which the valve core is installed into the valve body. These two structural forms each have their own advantages and disadvantages, which are briefly described as follows.

1. The "side mounted" structure is compact, the valve body is close to circular symmetry, and the overall rigidity is good. Due to the presence of the middle mouth, the "upper type" greatly destroys the rotational symmetry of the valve body. Under the axial force of the pipeline (including the medium force and the sealing pair force), asymmetric elastic deformation will occur, causing uneven deformation of the valve seat and reducing the fit of the sealing pair, leading to internal leakage. Therefore, it is not appropriate to use a "top up" design on valves with high pressure and large diameter.

2. Some manufacturers claim that the "upper installation" can be "repaired online", but only allows for the replacement of the sealing ring (rubber ring) on the valve core, while the valve seat sealing ring, like the side installation, is installed from outside the flange at the end of the valve body and cannot be replaced. However, during valve operation, the erosion of the valve seat is often more severe than that of the valve core, and replacement is more necessary. So, the claimed 'online repair' can only achieve partial functionality and is a non primary function. In engineering practice, there has never been an example of "online maintenance".

3. The "side mounted" valve, due to its good overall rigidity, can achieve bidirectional sealing, that is, the valve core spherical surface can be installed facing the fluid medium or installed in reverse, both of which can achieve reliable sealing. The upper type can only be installed facing away and sealed with the help of medium pressure. In the two-phase flow of "gas-solid" and "liquid-solid", when the valve is closed, solid phase medium will accumulate in the chamber of the valve body, causing space occupation and preventing the valve from opening.

Overall, eccentric hemispherical valves should be selected for use in suitable working conditions in order to fully utilize the valve's effectiveness.