Abstract: A hydraulic system comprises: a first fluid distribution line (A) and a second fluid distribution line (B) communicating with a stem chamber (11) of a double-acting cylinder (10) destined to move two reciprocally mobile parts; a third fluid distribution line (O) communicating with a single-acting cylinder (20) for blocking the mobile parts; a solenoid distributor (2) which intercepts the third line (O) and switches the third line (O) between a first position in which it pressurises the single-acting cylinder (20) and a second position in which it discharges the single-acting cylinder (20); a first bistable selector valve (7) sending in outlet a pressure signal when a pressure difference between the first line (A) and the second line (B) exceeds a certain value; a pressure sensor (8) communicating with the first selector valve (7) and associated to the solenoid distributor (2) such as to switch the solenoid distributor (2) into the second position when the fluid pressure coming from the outlet of the first