A filling device (101, 102, 103) adapt for filling a hydraulic system with a fluid mixture composed of at least a first fluid and a second fluid, said filling device comprising: a fluid mixture circuit for being connected to the hydraulic system to allow the fluid mixture to circulate therein; a pressure sensor connected to the fluid mixture circuit for detecting a pressure of the fluid mixture in the circuit and generating a first signal representing the pressure; a concentration sensor connected to the fluid mixture circuit for detecting a concentration of the second fluid in the fluid mixture and generating a second signal representing the concentration; a first incoming line connected to the fluid mixture circuit for introducing the first fluid from a first fluid resource to the circuit; a second incoming line connected to the fluid mixture circuit for introducing the second fluid from a second fluid resource to the circuit; and a controller electrically connected with the pressure sensor and the concentration sensor for receiving the first and the second signals and controlling the introduction of the first fluid and/or the second fluid via the first incoming line and/or the second incoming line based on the signals, characterized in that, a first outgoing line is connected to the fluid mixture circuit for extraction of the fluid mixture, and a first outgoing electric valve is connected in the first outgoing line; wherein the controller is electrically connected with the first outgoing electric valve and configured to enable said valve to open for extraction of the fluid mixture when a pressure detected via the pressure sensor exceeds a range of pressure target tolerance. a fluid mixture circuit for being connected to the hydraulic system to allow the fluid mixture to circulate therein; a pressure sensor connected to the fluid mixture circuit for detecting a pressure of the fluid mixture in the circuit and generating a first signal representing the pressure; a concentration sensor connected to the fluid mixture circuit for detecting a concentration of the second fluid in the fluid mixture and generating a second signal representing the concentration; a first incoming line connected to the fluid mixture circuit for introducing the first fluid from a first fluid resource to the circuit; a second incoming line connected to the fluid mixture circuit for introducing the second fluid from a second fluid resource to the circuit; and a controller electrically connected with the pressure sensor and the concentration sensor for receiving the first and the second signals and controlling the introduction of the first fluid and/or the second fluid via the first incoming line and/or the second incoming line based on the signals, characterized in that, a first outgoing line is connected to the fluid mixture circuit for extraction of the fluid mixture, and a first outgoing electric valve is connected in the first outgoing line; wherein the controller is electrically connected with the first outgoing electric valve and configured to enable said valve to open for extraction of the fluid mixture when a pressure detected via the pressure sensor exceeds a range of pressure target tolerance.