| 摘要 |
PROBLEM TO BE SOLVED: To stop operation of a boom when a mobile concrete pump with a boom is switched from low pressure operation to high pressure operation. SOLUTION: Hydraulic pistons 24, 24a in two main hydraulic cylinders 22, 23 are connected with pistons in two cylinders for pressure-feeding concrete through piston rods 14. A high/low selector valve 25 is disposed upstream where pressure oil is supplied to the two main hydraulic cylinders 22, 23, and sealing circuits 47, 48 are respectively disposed to a high pressure operation port a and a low pressure operation port b of the high/low selector valve 25. A pressure switch is disposed to detect pilot pressure acting on a side of the high pressure operation port a. If pressure detected by the pressure switch 52 is high, a solenoid SOL1 of a boom on load valve 53 is demagnetized to release the pressure oil from a hydraulic pump 54 for a boom into a pressure oil tank 57, so that a boom operating valve 55 becomes an inoperative state. COPYRIGHT: (C)2004,JPO&NCIPI
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