Hydraulic hammering device

A hydraulic hammering device comprising:

• a piston slidably fitted into a cylinder, the piston being configured to advance and retract to hammer a rod for hammering;
• a front chamber and a rear chamber that are defined between an outer peripheral surface of the piston and an inner peripheral surface of the cylinder and arranged separated from each other in a front and a rear direction;
• and
• a switching valve mechanism configured to switch the front chamber into communication with a low pressure circuit when the piston advances, and to switch the front chamber into communication with a high pressure circuit when the piston retracts, and to supply and discharge hydraulic oil so that an advance and a retraction of the piston can be repeated,
• wherein the front chamber has a front-chamber liner that is fitted to an inner surface of the cylinder,
• a hydraulic chamber space is formed in the front-chamber liner as a cushion chamber, the hydraulic chamber space communicating with the front chamber to be filled with hydraulic oil, and
• the cushion chamber has a second drain circuit that is formed separately from a first drain circuit, the first drain circuit configured to guide hydraulic oil passing a liner bearing section of the front-chamber liner, the separate second drain circuit positioned in front of the front chamber at a position in an axial direction between the liner bearing section and the front chamber, the second drain circuit configured to guide hydraulic oil to the low pressure circuit without passing through the first drain circuit.