Abstract: A hydraulic screw machine including a drive screw and at least one running screw co-operating therewith are arranged inside a housing, the drive screw being united with a shaft extending out through the housing at the high pressure side of the machine and being provided with a balancing piston for balancing a part of the axial force acting on the drive screw and also with a collar which together with a wall portion of the housing forms a hydrostatic axial bearing for taking up the remaining axial force acting on the drive screw. The bearing surfaces of the axial bearing are kept separated by a spring means during starting and similar operating conditions. An axially limitedly movable rolling bearing is mounted in association with the hydrostatic axial bearing and takes up axial forces on the drive screw occurring in certain operating conditions.

Abstract: A hydraulic screw machine comprises a driving screw and at least one impeller screw with a balance plunger at its end. The thread of the impeller screw is complete with full depth all the way to the balance plunger. The length of the plunger is less than the width in the axial direction of the thread groove in the driving screw. The balance plunger is mounted on an axial pin on the end of the impeller screw.