Breaker using pneumatic and hydraulic pressures

A breaker using pneumatic and hydraulic pressures, comprising a chisel, a chisel case receiving said chisel and guiding an axial movement of the chisel within a stroke, a cylinder assembled with the chisel case and coaxially receiving a piston used for hammering the chisel, and a gas chamber provided at an upper end of the cylinder and containing nitrogen gas and selectively compressing the nitrogen gas in response to an axial movement of the piston within the cylinder, further comprising:

• first and second stepped surfaces formed on an outer surface of said piston, thus changing an outer diameter of the piston and forming first and second chambers between the outer surface of the piston and an inner surface of the cylinder;
• a third chamber defined between the piston and the cylinder at a position between the first and second chambers;
• a first oil path formed in a sidewall of said cylinder and allowing an oil inlet port of the cylinder to communicate with said first chamber, thus feeding pressurized oil from an external oil source to the first chamber;
• a valve chamber formed in the sidewall of the cylinder while extending from the first oil path in a direction opposite to the first chamber;
• a second oil path formed in the sidewall of the cylinder so as to allow the valve chamber to selectively communicate with the second chamber;
• a directional control valve unit installed within said valve chamber and used for selectively returning the pressurized oil from the first chamber to the valve chamber prior to feeding the pressurized oil from the valve chamber to the second chamber through a plurality of oil ports thereof and said second oil path;
• a third oil path formed in the sidewall of the cylinder at a position between said first and second oil paths, and selectively communicating with the valve chamber through said valve unit in response to an axial movement of the piston within the cylinder;
• and
• a fourth oil path formed in the sidewall of the cylinder at a position around the third oil path, and used for discharging the pressurized oil from the third chamber through an oil drain path, thus making the pressure of the third chamber become zero and initializing the pressure of the third chamber.