Rock breaking device, protection valve and a method of operating a rock breaking device

A protection valve comprising:

• a body,
• at least one inlet opening for feeding hydraulic fluid to a protection valve,
• at least one outlet opening for feeding hydraulic fluid from the protection valve to the inlet channel of a hydraulic auxiliary device,
• a spool arranged to move in the inlet direction of the flow and in the reverse direction of the flow,
• at least one force member for moving the spool towards the inlet direction,
• at least one control pressure surface in the spool, the pressure of the pressure fluid influencing the control pressure surface being arranged to generate a force to move the spool axially,
• at least one collar in the spool, the collar being arranged to open and close a connection between the inlet opening and the outlet opening,
• the spool comprises at least one first control pressure surface in continuous connection with the pressure in the inlet opening and arranged to influence the spool in the reverse direction,
• the spool comprises at least one second control pressure surface in continuous connection with the pressure in the outlet opening and arranged to influence the spool in the inlet direction,
• the outlet opening is provided with at least one throttle to provide a pressure difference between the inlet opening and the outlet opening, the magnitude of the pressure difference being dependent on the magnitude of the fed volume flow,
• the magnitude of the resultant force of the first control pressure surface and the second control pressure surface in the reverse direction is dependent on said pressure difference,
• the axial position of the spool is arranged to be determined on the basis of the mutual relation of said resultant force and the force provided by a force member,
• the spool of the protection valve has three predetermined axial coupling points,
• at the first coupling point a first collar of the spool is arranged to prevent a pressure fluid flow from the inlet opening to the outlet opening,
• at the second coupling point there is an open connection from the inlet opening to the outlet opening when the resultant force and the force provided by the force member, influencing the spool, are in balance,
• and wherein at the third coupling point a second collar of the spool is arranged to prevent, at least partly, pressure fluid flow from the inlet opening to the outlet opening when the resultant force influencing the spool is greater than the force provided by the force member.

A method of operating a hydraulic rock breaking device, the method comprising:

• feeding hydraulic fluid along an inlet channel in the inlet direction of the flow to a percussion device of a rock breaking device to generate and transmit impact pulses to a tool connected to the rock breaking device,
• controlling the operating cycle of the percussion device by means of at least one control valve,
• preventing, by means of at least one valve, pressure fluid from flowing back in the reverse direction when the percussion device has been stopped,
• leading the pressure fluid flowing to the percussion device through at least one protection valve in the inlet direction,
• monitoring the volume flow of the pressure fluid fed to the percussion device by means of said protection valve,
• and preventing, at least partly, pressure fluid flow through the protection valve if the volume flow fed to the percussion device exceeds a preset maximum volume flow determined by the protection valve.