A hydraulic compression tool 2 having a frame 13, a hydraulic fluid reservoir 8 on the frame, a ram 16 movably connected to the frame, a conduit system in the frame between the reservoir 8 and the ram 16, a pump 24 provided in the conduit system, a mechanical actuator 66 provided in the conduit system for contacting the ram 16, and a bypass valve 72 in the conduit system between a rear end 96, 100 of the ram 16 and a channel 46 of the conduit system to the rear end of the mechanical actuator 66. The conduit system is adapted to conduit fluid from the pump 24 against both the rear end 96, 100 of the ram 16 and a rear end 74 of the mechanical actuator 66. The bypass valve 72 is located, at least partially, in a housing member 70 of the mechanical actuator 66.

A hydraulic compression tool 2 having a frame 13, a hydraulic fluid reservoir 8 on the frame, a ram 16 movably connected to the frame, a conduit system in the frame between the reservoir 8 and the ram 16, a pump 24 provided in the conduit system, a mechanical actuator 66 provided in the conduit system for contacting the ram 16, and a bypass valve 72 in the conduit system between a rear end 96, 100 of the ram 16 and a channel 46 of the conduit system to the rear end of the mechanical actuator 66. The conduit system is adapted to conduit fluid from the pump 24 against both the rear end 96, 100 of the ram 16 and a rear end 74 of the mechanical actuator 66. The bypass valve 72 is located, at least partially, in a housing member 70 of the mechanical actuator 66.

A hydraulic raising apparatus with automatic regulated speeds can automatically adapt its raising speeds for various load conditions. It mainly comprises additional hydraulic circuits, check valves and adjustable relief valves arranged between the piston rod side chamber and the rodless side chamber of hydraulic cylinders and pumps. The arrangement enables hydraulic cylinders and pumps to change their working modes in a hydraulic circuit, depending on loaded conditions, from a piston type to a spool type and vice versa. Hence the hydraulic apparatus can adjust its raising speeds in agreement with loads. When the apparatus bears a light load, it will quickly carry the load to position. On the other hand, when the load is heave the apparatus will move it at a slower speed and thus need just reduced input energy. Therefore, the apparatus according to the invention can enhance efficiency to the greatest extent.

A hydraulic circuit system for a jack comprises an inlet circuit, a return circuit and an overload protection circuit with a piston-cylinder assembly (4,10), a sequence valve (B), a safety valve (D) and a relief valve (C), the inlet circuit extending from an outer reservoir (2) via a check valve (A1) to an oil chamber (3) of a manual pump (20), the oil chamber (3) being connected to an inner oil chamber (41) formed in the piston rod (4) via another check valve (A2) to form a closed circuit. The oil chamber (3) of the pump (20) is connected to an inner reservoir (1) in the hydraulic cylinder (10) via a sequence valve (B), and the inner reservoir (1) is connected to the outer reservoir (2) via a check valve (A3). When the maximum effect capacity of the oil chamber (3) of the pump (20) is greater than or equal to that of the inner oil chamber (41) of the piston rod (4), a single touch of the pump (20) can raise the hydraulic jack to a required loading position under no load or light load conditions.