Valve arrangement

A valve device for automatic adjustment of the fluid pressure to a hydraulic tightening piston is a sawing gear between a holder and a saw bar displaceable in a longitudinal direction relative to the holder for adjusting the tightness of a saw chain running around the saw bar and a wheel positioned on the holder, the tightening piston being connected to a hydraulic system via the valve device, the valve device includes a cylindrically-shaped space and a displaceable piston dimensioned to fit and move between forward and rearward stop positions within the space, the improvement characterized in that the space in front of the piston has first and second opening connections, said first opening connection or inlet to the hydraulic system and said second opening connection or outlet to the tightening piston, an openable check valve being positioned in the outlet such that said check valve allows fluid to flow only in one direction from the cylindrically-shaped space to the tightening piston, the displaceable piston being under tension by a spring and urged in a forward direction towards the outlet and the forward stop position causing the check valve to move to an open position, whereby the displaceable position, when the hydraulic system is in a non-pressurized state, is caused by the influence of the spring to its forward stop position opening the check valve, and when the hydraulic system is in a pressurized state, is pushed back by the pressure in said cylindrically-shaped space to its rearward position which permits the check valve to close preventing hydraulic fluid from flowing from the tightening piston and into the cylindrically-shaped space.