Abstract: In a device and a method for a tree harvester head for trimming tree trunks, the device includes a frame (1) supporting feed rollers (2), one or more trimming knives (4) that pivot towards and away from the tree trunk, as well as a trimming knife (6) permanently fixed to the frame (1) and with a radius of curvature that is essentially equivalent to the radii of curvature of the pivoting trimming knives (4).

Abstract: A hydraulic stretching device for a saw chain active in sawing apparatus having a saw bar and including a holder (1), a driving wheel (3) for the saw chain arranged essentially stationary in relation to the holder and a guiding part (7) permanently arranged at a saw bar to interact with the holder (1). The guiding part (7) is permanently attached to resist turning and axially displaceable in relation to the holder (1) in the longitudinal direction (8) of the saw bar to allow stretching of a saw chain running round the saw bar (6) and the driving wheel (3). The stretching device for a saw chain is arranged to be active between the holder (1) and the guiding device (7) and including a hydraulically influenced piston (10). The piston (10) is arranged in a displaceable manner at the holder in parallel with the longitudinal direction (8) of the saw bar and has an engaging surface (11) intended to engage an opposing surface (12) on the guiding part (7).

Abstract: A valve device including a cylindrically-shaped space and a displaceable piston dimensioned to fit and move between forward and rearward stop positions within the space, having a first opening connection or inlet to the hydraulic system and a second opening connection or outlet to the tightening piston in the space and an openable check valve positioned in the outlet such that the check valve allows fluid to flow only in one direction from the cylindrically-shaped space to a hydraulic tightening piston in a sawing gear for adjusting the tightness of a saw chain.