Abstract: A hydraulic drive circuit for a load-handling machine such as hydraulic crawler crane, shovel or the like in which the maximum output pressure of the circuit is determined by a main relief valve provided on the delivery side of a hydraulic pump. The drive circuit is capable of producing a surge of power or output by automatically increasing the relief pressure of the main relief valve above a rated pressure of the circuit for a short time period of about a few seconds, when required for extracting an implanted pile, for pulling a bucket which is caught on a large stone, or for getting a machine out of a muddy spot. At the end of the predetermined time period, the circuit pressure is automatically returned to the level of the rated pressure. The surge output is from 130% to 150% of the rated output but allows use of hydraulic components or an engine of a capacity designed for the rated output without troubles or engine stops.