JPS648128A - Up-and-down float device for unloader - Google Patents

Abstract

PURPOSE:To obtain an up-and-down float device for an unloader without possibility of its boom end being damaged, by interposing an open-close changeover valve in a connection passage and further interposing in the same connection passage a check valve and a flow rate control valve in parallel. CONSTITUTION:In the case a vessel lowers, a main boom 35 receives a force tending to narrow its tilt angle relative to a support column while a cylinder 39 receives a force in the direction to retract a rod 39b. At this time, pressure oil in an oil pressure chamber 54 on the head side flows out to an oil passage 53 where a check valve 61 is interposed and further to a connection passage 55. The pressure oil which has flowed in is forced to flow, as the check valve 58 works, on the side of a flow rate control valve 57 and returns via a changeover valve 56 and an oil passage 51 to an oil pressure chamber 52 located on the rod side. At this time, the velocity of the pressure oil is made to the value determined with the flow rate control valve 57. As a result, the moving speed of the boom 35 can be made to an appropriate value which is slower than the lowering speed of the vessel by appropriately determining the setting pressure of the flow rate control valve 57.