| 摘要 |
A hydraulic circuit of working truck comprising a traveling body (1), a slewing body (2) provided turnably on the traveling body (1), hydraulic sources (21, 28) provided on the slewing body (2), a plurality of hydraulic cylinders (11) for work provided on the traveling body (1) to be driven with pressure oil from the hydraulic sources (28), a control valve (22) for controlling the flow of pressure oil from the hydraulic sources (28) to the hydraulic cylinders (11) for work, an operating means (26) for commanding the control valve (22) to be driven, valve units (12a, 12b) with check valve provided in association with the plurality of hydraulic cylinders (11) for work and permitting/blocking outflow of pressure oil from each hydraulic cylinder (11) for work, means (41, 42) for delivering a telescopic action permitting command or a telescopic action prohibiting command to each hydraulic cylinder (11) for work, and means (34-36, 43-48) for controlling the valve units (12a, 12b) such that the function as a check valve is made ineffective upon delivery of the telescopic action permitting command from the commanding means (41) to allow outflow of pressure oil from the hydraulic cylinders (11) for work and to block outflow of pressure oil from the hydraulic cylinders (11) for work by means of the check valve upon delivery of the telescopic action prohibiting command.
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