Hydraulic circuit for cylinder.

摘要

Described herein is a hydraulic circuit suitable for use on power shovel or other construction machines, more specifically a hydraulic circuit for a cylinder in hydraulic power transmission of the type which is adapted to control pressurized oil flows to and from two oil chambers in the cylinder (4) by switching the position of a directional control valve (2) in communication with a pressurized oil source (35), the hydraulic circuit comprising: a logic valve (5) provided between the directional control valve (2) and a load-holding oil chamber in the cylinder (42), and having first (51) and second ports (52) connected to the directional control valve (2) and said load-holding oil chamber (42), respectively; and a selector valve (6) operable in relation with the switching of the directional control valve (2) to communicate a spring chamber (55) of the logic valve (5) with a conduit between the first port (51) and the directional control valve (2) in an operational phase of supplying pressurized oil to a load lowering chamber (41) of the cylinder (4) and to communicate the spring chamber (55) with the second port (52) in other operational phases.