Hydraulic circuit for heavy equipment having variable control device

摘要

The hydraulic circuit includes at least one variable displacement hydraulic pump (1); a main relief valve (2) installed on an upstream side of a discharge flow path of the hydraulic pump; an option attachment (3) connected to the hydraulic pump (1); a main control valve (5) installed in a flow path between the hydraulic pump (1) and the option attachment (3); port relief valves (12,13), installed inside the main control valve (5), for being proportionally controlled so as to variably control relief pressure required for the option attachment in accordance with pilot signal pressure inputted from an outside; and a proportional relief valve (14), installed outside the main control valve (5), for variably controlling the pilot signal pressure inputted to the port relief valves (12,13) in accordance with an electric signal inputted from an outside.