| 摘要 |
<p>PURPOSE:To enable performing of an easy switching operation with an extremely simple structure, by a method wherein a pilot check valve is placed between sweeping rooms at opposite ends of a piston, and the piston is positioned so that it can be switched in both directions by alternately operating the valve by means of an oil pressure signal. CONSTITUTION:In the case of the expansion of an oil jack, a switch valve 4 is set at a position 4A, and a discharge oil pressure is transmitted to a sweeping chamber 1d through a check valve 3c with a manual pump 5 actuated. A pilot check valve 3e is opened with the discharge oil pressure fed through a pilot tube 4e and ports 4c and 4a, and thereby an oil pressure in a pipe line 3b is fed through the valve 3e to a sweeping chamber 1e as well. Thus, a piston 2 moves to the left due to a difference in a pressure acting area. In the meantime, in order to contract the jack from a state described above, that is, to move the piston 2 to the right, the switch valve 4 is switched to a position 4B, and the discharge oil pressure from the manual pump 5 is fed to only the sweeping chamber 1d.</p> |
