| 摘要 |
A hydraulic jack having a piston and a cylinder in which the piston has at its head a cavity the dimensions of the cavity and the constructional materials of the cylinder and the piston being selected so that hydraulic pressure applied within the cylinder acts to deform the cylinder wall and the parts of the piston defining the cavity in such a manner that, over the normal rate of operating pressures of the jack the clearance between the piston and the cylinder remains within the capacity of the sealing means arranged between the piston and the cylinder to provide an effective seal. |
