A hydraulic circuit of a return line of heavy equipment is provided to minimize the energy of a hydraulic system by back pressure occurring in a return line and to reduce the energy for the entire equipment by varying and controlling back pressure occurring in a return line of a hydraulic system according to working conditions. A hydraulic circuit of a return line of heavy equipment comprises a hydraulic pump(10) operated by an engine, an actuator(30) connected to the hydraulic pump and operated by hydraulic fluids, a control valve(20) installed to a flow path between the hydraulic pump and the actuator and controlling the startup, stop and directional change of the actuator by a spool converted by getting supplied with signal pressure from the outside, a first variable check valve(50) and an oil cooler(40) installed to a flow path between the control valve and a hydraulic tank(70), a first return line(L1) varying the preset pressure of hydraulic fluids passing through the first variable check valve according to the supplied signals and returning to the hydraulic tank via the oil cooler, a second variable check valve(60) installed to a flow path connected with the first return line, and a second return line(L2) varying the preset pressure of hydraulic fluids passing through the second variable check valve and returning to the hydraulic tank, wherein the first and second variable check valves are operated by inputting electrical signals from a CPU(central processing unit)(80).
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