Patent ID: 8118112

Claim:
A hydraulic rock breaking device comprising: a percussion device arranged to generate impact pulses in a tool connected to the rock breaking device; an inlet channel along which hydraulic fluid is feedable to the percussion device in the inlet direction of the flow; at least one protection valve arranged in the inlet channel, the protection valve comprising: a body; at least one inlet opening for feeding hydraulic fluid to the protection valve; at least one outlet opening for feeding hydraulic fluid from the protection valve to the inlet channel; a spool arranged to move in the inlet direction of the flow and in the reverse direction of the flow; and at least one force member for moving the spool towards the inlet direction, and wherein the spool of the protection valve has three predetermined axial coupling points, the spool is arranged to become positioned at the first coupling point by the effect of the force member in a situation where the inlet opening is provided with pressure lower than a predetermined pressure, whereby the protection valve is arranged to prevent at the first coupling point the flow of the pressure fluid in the reverse direction, the spool is arranged to become positioned at the second coupling point in a situation where a flow smaller than a predetermined maximum volume flow is led through the protection valve in the inlet direction, whereby the protection valve is arranged at the second coupling point to allow a pressure fluid flow through the protection valve, and the spool is arranged to become positioned at the third coupling point in a situation where a flow larger than a predetermined maximum volume flow is led through the protection valve in the inlet direction, whereby the protection valve is arranged at the third coupling point to prevent, at least partly, pressure fluid flow through the protection valve.