| 摘要 |
PROBLEM TO BE SOLVED: To easily change the set compensation pressure of a pressure compensating means according to changes of the set charging pressure of an oil pressure chamber for absorbing an overload. SOLUTION: A hydraulic pump 5, an overload preventing valve 10 and a pressure compensating means 14 are connected in parallel to an oil pressure chamber 3 for absorbing an overload in the slide 2 of a mechanical press 1, and a check valve 9 stopping a flow to the hydraulic pump 5 is provided. The pressure compensating means 14 is constituted by a choke path 26 and a relief valve 27 connected in series so that a relief operation is obtained when the pressure of the oil pressure chamber 3 rises at a very slow speed. The relief valve 27 is pressed to a closing position X by the resultant force of a valve closing force based on the pressure of the inlet side 9a of the check valve 9 and the valve closing force of a compression spring 29 for keeping a residual pressure, and it is also pressed to an opening position Y by a valve opening force based on the pressure of the outlet side 31 of the choke path 26.
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