| 摘要 |
A control circuit (11, 11b) for a fluid pressure-operated cylinder (13, 13b) or the like has a quick-drop valve (12, 12b) which enables faster gravity-assisted lowering of a load (16, 16b) and which quickly shifts to a power-down mode of operation whon dropping of the load by gravity ceases. Means (47, 47b, 54, 54b, 56, 56b) sensing flow rate to the head end of the cylinder and sensing cavitation in the head end initiate the quick-drop operation at which the discharge path from the cylinder back to tank is totally blocked and all discharge from the rod end is recirculated to the head end. When resistance to further lowering of the load occurs, the quick-drop valve responds by shifting to block communication betwesn ends of the cylinder while establishing a rod end discharge path to tank to initiate a power-down mode of operation quickly and without lag or bounce.
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