Breaker for excavator comprising: - a body inside which a hydraulic circuit is formed which can be supplied from outside with liquid under pressure, said hydraulic circuit comprising: - an inlet for the liquid under pressure; - an outlet for the return of the liquid under pressure to the supplying circuit; - an active thrust chamber and a passive thrust chamber; - ducts (12, 21) to connect said active thrust chamber and said passive thrust chamber to said inlet; - a piston configured so that it can slide in a reciprocating motion inside said breaker under the thrust of said liquid under pressure, said piston being provided, at the active thrust chamber, with a projection having a diameter smaller than the diameter of the active thrust surface, said projection being wholly contained inside the active thrust chamber, - a tool coaxially positioned to said piston and configured to slide axially between a first and a second position; - a distributor, positioned concentrically to said piston and configured to slide axially putting in communication, alternatively, the active thrust chamber with the high pressure portion or the low pressure portion of the hydraulic circuit, said distributor being configured to assuming at least a position where the distributor is inserted around the piston; Characterized in that Said breaker further comprises - a bypass between said ducts (12, 21) which connects said thrust chambers (11, 20) to said inlet and outlet, configured so that said bypass is free when the piston is in a position with an axial excursion greater than a predetermined limit position; - an accumulator comprising a first volume connected to said circuit containing the liquid under pressure and a second volume separated from said first volume by an elastic membrane and in that said piston and said projection are configured so that the liquid under pressure can act on a circular surface defined by the diameter of said active thrust chamber. - a body inside which a hydraulic circuit is formed which can be supplied from outside with liquid under pressure, said hydraulic circuit comprising: - an inlet for the liquid under pressure; - an outlet for the return of the liquid under pressure to the supplying circuit; - an active thrust chamber and a passive thrust chamber; - ducts (12, 21) to connect said active thrust chamber and said passive thrust chamber to said inlet; - an inlet for the liquid under pressure; - an outlet for the return of the liquid under pressure to the supplying circuit; - an active thrust chamber and a passive thrust chamber; - ducts (12, 21) to connect said active thrust chamber and said passive thrust chamber to said inlet; - a piston configured so that it can slide in a reciprocating motion inside said breaker under the thrust of said liquid under pressure, said piston being provided, at the active thrust chamber, with a projection having a diameter smaller than the diameter of the active thrust surface, said projection being wholly contained inside the active thrust chamber, - a tool coaxially positioned to said piston and configured to slide axially between a first and a second position; - a distributor, positioned concentrically to said piston and configured to slide axially putting in communication, alternatively, the active thrust chamber with the high pressure portion or the low pressure portion of the hydraulic circuit, said distributor being configured to assuming at least a position where the distributor is inserted around the piston; - a tool coaxially positioned to said piston and configured to slide axially between a first and a second position; - a distributor, positioned concentrically to said piston and configured to slide axially putting in communication, alternatively, the active thrust chamber with the high pressure portion or the low pressure portion of the hydraulic circuit, said distributor being configured to assuming at least a position where the distributor is inserted around the piston; - a bypass between said ducts (12, 21) which connects said thrust chambers (11, 20) to said inlet and outlet, configured so that said bypass is free when the piston is in a position with an axial excursion greater than a predetermined limit position; - an accumulator comprising a first volume connected to said circuit containing the liquid under pressure and a second volume separated from said first volume by an elastic membrane and in that said piston and said projection are configured so that the liquid under pressure can act on a circular surface defined by the diameter of said active thrust chamber.