A boom arrangement (1) having a hydraulic system (10) comprising an electrically controlled first shutoff valve (19) arranged in a first pipeline (17), an electrically controlled second shutoff valve (20) arranged in the first pipeline (17), a first bypass pipeline (21) connected to the first pipeline (17) for bypassing the first shutoff valve (19), a first check valve (22) arranged in the first bypass pipeline (21), a second bypass pipeline (23) connected to the first pipeline (17) for bypassing the second shutoff valve (20), and a second check valve (24) arranged in the second bypass pipeline (23). An electric operating switch (25, 26) is arranged in the cab of the work machine to be operated by the driver of the work machine, for opening and closing the electrically controlled first shutoff valve (19) and second shutoff valve (20). In the method, the hydraulic system (10) is operated as a closed circuit, successive pulses of hydraulic fluid flow are generated, either the first (11) or the second shutoff valve (14) is closed, such that the flow of hydraulic fluid runs in only one direction in the first pipeline (17) through the bypass flow channel (21 or 23) bypassing the shutoff valve that is closed, the check valve (22 or 24) in said bypass flow channel preventing the fluid flow in the opposite direction, whereby the side booms (6, 8) are turned, and the closed first shutoff valve (19) or second shutoff valve (20) is opened, or both of the shutoff valves are closed, when the side booms have turned to the desired tilt angle.
