| 摘要 |
PROBLEM TO BE SOLVED: To restrain dispersion of a stopping position to the minimum extent by arranging a check valve and a stop valve in parallel between a hydraulic pump and a pilot check valve, and controlling the stop valve by a solenoid valve for the stop valve which uses pressure in a hydraulic cylinder as pilot pressure. SOLUTION: In a descending process of a hydraulic elevator, a solenoid valve 23 for a descent is turned on, and when its position is switched to (b) from (a), pressure of an operating fluid so far pushing up a ram 11 in a cylinder 10 opens a pilot check valve 7, and the operating fluid reaches a stop valve 8. The operating fluid also returns to a tank 20 by rotating a hydraulic pump 1 as a hydraulic motor. At this time, it is transferred to a high speed descent by controlling a frequency of an inverter motor 2, and next, though descending speed of the ram 11 is reduced by controlling a frequency imparted to the motor 2, when the frequency of the motor 2 is set to about 1Hz or less, the solenoid valve 23 is turned on, and its position is switched to (d) from (c), and the stop valve 8 is closed, and a descent of the ram 11 is stopped. |
