Abstract: A power wrench (10) for turning a screw is supplied by a hydraulic unit (25) that contains a positive displacement pump (26) and supplies a defined rate of flow. The pressure in a hydraulic pressure line (28) is measured by a pressure sensor (32) and provided to a control unit (31). The volume flow of the hydraulic unit (25) is determined in amount per unit of time. The piston stroke per unit of time can be determined due to the fact that the filling volume of the hydraulic cylinder is known. The piston acts upon a lever system that turns the moving part. The turning angle per unit of time can be determined due to the fact that the lever length is known. This makes it possible to dispense with an angle measuring device and to determine the turning angle merely by measuring pressure.

Abstract: A power wrench (10) for turning a screw is supplied by a hydraulic unit (25) that contains a positive displacement pump (26) and supplies a defined rate of flow. The pressure in a hydraulic pressure line (28) is measured by a pressure sensor (32) and provided to a control unit (31). The volume flow of the hydraulic unit (25) is determined in amount per unit of time. The piston stroke per unit of time can be determined due to the fact that the filling volume of the hydraulic cylinder is known. The piston acts upon a lever system that turns the moving part. The turning angle per unit of time can be determined due to the fact that the lever length is known. This makes it possible to dispense with an angle measuring device and to determine the turning angle merely by measuring pressure.