PROBLEM TO BE SOLVED: To shorten a time lag which occurs in fast lowering a reaping part.SOLUTION: A hydraulic circuit for elevating/lowering a reaping part of a combine comprises: a pilot operated check valve 11 a first throttle 9 for limiting a flow rate of a hydraulic solution supplied from a hydraulic pump 4 to a hydraulic cylinder 2, the first throttle 9 being connected in parallel with a first switching valve 7 a resistor valve 10 which is connected in series with the first throttle 9 and opened when primary-side oil pressure reaches predetermined pressure a second throttle 12b for limiting the flow rate of the hydraulic solution drained by flowing back through the pilot operated check valve 11 a third throttle 18 for limiting the flow rate of the hydraulic solution to be drained, the third throttle 18 having the channel sectional area being smaller than that of the second throttle 12b and a second switching valve 19 capable of selectively switching an oil passage of the hydraulic solution to be drained to an oil passage of the hydraulic solution to be drained through the third throttle 18.COPYRIGHT: (C)2014,JPO&INPIT【課題】 刈取部を高速で下降させる際に生じるタイムラグを短縮する。【解決手段】 パイロット操作型チェック弁11と、第1の切換弁7と、第1の切換弁7と並列に接続され、油圧ポンプ4から油圧シリンダー2へ供給される作動油の流量を制限するための第1の絞り9と、第1の絞り9と直列に接続され、一次側油圧が所定圧力に達したときに開弁する抵抗弁10と、パイロット操作型チェック弁11を逆流してドレンされる作動油の流量を制限するための第2の絞り12bと、第2の絞り12bより流路断面積が小さく、ドレンされる作動油の流量を制限するための第3の絞り18と、ドレンされる作動油の油路を、第3の絞り18を通じてドレンされる作動油の油路に選択的に切換可能な第2の切換弁19と、を備える。【選択図】 図2
