Abstract: Hemispherical hydraulic cylinder is the key part of hydraulic press with unity of cylinder and beam(HPUCB). Comparing with the cylindrical hydraulic cylinder used in traditional three beams four pillars hydraulic press, it can support approximately two times liquid pressure due to the significant changes in structure and stress state. Strength calculation equation for hemispherical hydraulic cylinder is derived. For the thick-walled spherical shell, the weakest zone is located on the inner wall where the algebraic value of radial stress is smallest(the absolute value is largest) and the latitudinal tensile stress and longitude tensile stress are biggest. The equivalent stresses calculated through 3rd strength theorem or 4th strength theorem are the same, and it should be less than the allowable stress of the material. Comparing with strength calculation equation between hemispherical hydraulic cylinder and cylindrical hydraulic cylinder under the condition of the same liquid pressure, the same inner radius and the same allowable stress, it can be seen that thickness of hemispherical hydraulic cylinder is much less than the cylindrical hydraulic cylinder, and the effect of reducing weight is obvious.

Key words: Cylindrical hydraulic cylinder, Hemispherical hydraulic cylinder, Hydraulic press, Unity of cylinder and beam