Hydraulic circuit for pipe layer

Abstract

Disclosed is a hydraulic circuit for a pipe layer, in which the generation of hydraulic shock in equipment is prevented when an operating device or a moving device is finely operated during combined work in a pipe-laying operation mode. The hydraulic circuit for a pipe layer according to the present invention comprises a main control valve having a straight traveling valve and controls a discharged flow of a hydraulic pump by a negative flow control system, wherein the hydraulic circuit comprises: an unloading valve which linearly controls the closing of a passage of a flow that flows to a hydraulic tank from a center bypass passage of a hydraulic pump when an operating device or a moving device is finely operated during combined work; a pilot valve which is linked with a straight traveling valve, and supplies signal pressure corresponding to an operation signal of the moving device or the operating device to the unloading valve; and an operation mode switch valve which is switched during the combined work, and respectively supplies pilot signal pressure to the straight traveling valve, the pilot valve, and a valve spool which is installed on a downstream side of the center bypass passage of the hydraulic pump.