An hydraulic system for an autonomous multi-set pipeline isolation tool comprising an hydraulic piston; a pump for operating the pistons; an accumulator between each of the hydraulic pistons and the pump; and means for operating the pump. The system also comprises a manifold operable to control the flow of fluid in fluid pipelines to control the operation of the pistons which actuate gripping and sealing means of the autonomous multi-set pipeline isolation tool. The hydraulic system further comprises a controller comprising a number of operational modules which are positioned on a single printed circuit board. The advantage of this is that the size of the hydraulic system may be minimized thereby enabling use of the system within a pipeline having an inner diameter of the order of 0.15 m (6″) and upwards. The manifold of the hydraulic system is also provided with a triple fail safe redundancy mechanism.