CONTROL CIRCUIT FOR HYDRAULIC CYLINDER IN CONSTRUCTION MACHINE

摘要

PROBLEM TO BE SOLVED: To eliminate a shock when a hydraulic cylinder reaches the limits of extension and contraction strokes, in a simple and low cost structure. SOLUTION: While a proximal switch 27 to detect that a rear boom reaches to a speed regulation area at a little near side of the upper limit position is provided, a solenoid changeover valve 21 to convert the oil passage depending on the detection of the proximal switch 27; a pressure reduction valve 22 to reduce a pilot pressure; and a flow rate control valve 23 to delay the speed of the pressure reduction by the pressure reduction valve 22; are provided to a pilot oil passage to feed the pilot pressure at an extension side of the control valve 18 for a cylinder 11 for boom.