A pressure booster is equipped with a pair of cylinders provided on both sides of a center unit, pistons each disposed inside the pair of cylinders, and a piston rod connecting the pistons. Each of the cylinders has a drive chamber and a booster chamber partitioned by the piston therein, and wherein the pressure booster is further equipped with a switching valve that is switched by abutting on each of the pistons, and a reset valve disposed in a fluid passage connecting a supply port to one of the pair of drive chambers.

A pressure booster is equipped with a pair of cylinders provided on both sides of a center unit, pistons each disposed inside the pair of cylinders, and a piston rod connecting the pistons. Each of the cylinders has a drive chamber and a booster chamber partitioned by the piston therein, and wherein the pressure booster is further equipped with a switching valve that is switched by abutting on each of the pistons, and a reset valve disposed in a fluid passage connecting a supply port to one of the pair of drive chambers.

A proportional control fluid actuator that is used as a positioning device in applications such as a hydraulic directional control valve. The activating device has a cylinder body attachable to a valve body and has a bore carrying a piston that is coaxially secured to an end of a valve spool. The device is provided with spaced openings in the cylinder body that communicate with the bore therein to introduce fluid to act on opposite sides of the piston. Factory pre-compressed spring means are provided for normally urging the piston and spool to a center position. Since the areas of the fluid pressure applied on both sides of the piston are different (due to a spool on one side of the piston), two pre-compressed springs are used to compensate the area difference to achieve a proportional movement of the spool.

A proportional control fluid actuator that is used as a positioning device in applications such as a hydraulic directional control valve. The activating device has a cylinder body attachable to a valve body and has a bore carrying a piston that is coaxially secured to an end of a valve spool. The device is provided with spaced openings in the cylinder body that communicate with the bore therein to introduce fluid to act on opposite sides of the piston. Factory pre-compressed spring means are provided for normally urging the piston and spool to a center position. Since the areas of the fluid pressure applied on both sides of the piston are different (due to a spool on one side of the piston), two pre-compressed springs are used to compensate the area difference to achieve a proportional movement of the spool.

Pressure compensating valves not fully closing at the stroke end are employed, and upon the operator's operation for the traveling, pilot primary pressure is reduced and supplied to remote control valves 34c-34h of non-travel operating devices. Thus, the inflow of the hydraulic fluid into non-travel actuators is suppressed and a necessary amount of hydraulic fluid for travel motors is secured in travel combined operation. Accordingly, when saturation occurs in a construction machine's hydraulic drive system performing the load sensing control due to combined operation with a great load pressure difference between two actuators, deceleration/stoppage of an actuator on the low load pressure side is prevented by preventing full closure of the pressure compensating valve on the low load pressure side, while also preventing deceleration/stoppage of a high load pressure actuator by securing a necessary amount of hydraulic fluid for the high load pressure actuator.

Pressure compensating valves not fully closing at the stroke end are employed, and upon the operator's operation for the traveling, pilot primary pressure is reduced and supplied to remote control valves 34c-34h of non-travel operating devices. Thus, the inflow of the hydraulic fluid into non-travel actuators is suppressed and a necessary amount of hydraulic fluid for travel motors is secured in travel combined operation. Accordingly, when saturation occurs in a construction machine's hydraulic drive system performing the load sensing control due to combined operation with a great load pressure difference between two actuators, deceleration/stoppage of an actuator on the low load pressure side is prevented by preventing full closure of the pressure compensating valve on the low load pressure side, while also preventing deceleration/stoppage of a high load pressure actuator by securing a necessary amount of hydraulic fluid for the high load pressure actuator.

A pressing tool for plastically deforming a tubular workpiece. The pressing tool comprises a drive, a reservoir for providing a hydraulic fluid, a coupling interface for coupling the pressing tool to a pressing jaw assembly, and a hydraulic pump valve apparatus. The hydraulic pump valve apparatus comprises a pressure cylinder, an operating cylinder, and a pressure-relief valve element which is adapted to open a fluidic passage from the operating cylinder to the reservoir when a predefined maximum pressing pressure is reached and keep it open until the operating piston has returned to a first position.

A pressing tool for plastically deforming a tubular workpiece. The pressing tool comprises a drive, a reservoir for providing a hydraulic fluid, a coupling interface for coupling the pressing tool to a pressing jaw assembly, and a hydraulic pump valve apparatus. The hydraulic pump valve apparatus comprises a pressure cylinder, an operating cylinder, and a pressure-relief valve element which is adapted to open a fluidic passage from the operating cylinder to the reservoir when a predefined maximum pressing pressure is reached and keep it open until the operating piston has returned to a first position.

A pressure booster is equipped with a pair of cylinders provided on both sides of a center unit, pistons each disposed inside the pair of cylinders, and a piston rod connecting the pistons. Each of the cylinders has a drive chamber and a booster chamber partitioned by the piston therein, and wherein the pressure booster is further equipped with a switching valve that is switched by abutting on each of the pistons, and a reset valve disposed in a fluid passage connecting a supply port to one of the pair of drive chambers.

A pressure booster is equipped with a pair of cylinders provided on both sides of a center unit, pistons each disposed inside the pair of cylinders, and a piston rod connecting the pistons. Each of the cylinders has a drive chamber and a booster chamber partitioned by the piston therein, and wherein the pressure booster is further equipped with a switching valve that is switched by abutting on each of the pistons, and a reset valve disposed in a fluid passage connecting a supply port to one of the pair of drive chambers.