A valve system for use in a wellbore includes a side pocket mandrel and one or more well tools, where the side pocket mandrel includes an elongated body section provided with a connector at its ends, the elongated body section being provided with a substantially fully open main bore for alignment with the well tubing and an offset side pocket bore. At least one through opening is provided in the side pocket mandrel, leading into the side pocket bore, and at least one through opening is provided in the internal wall, leading into the main bore, where the at least two openings are in fluid communication through the side pocket bore, in which side pocket bore at least two valves are arranged in series to form a double fluid barrier between the main bore and an outside of the pocket mandrel, the at least two valves being independently retrievable through at least one installation opening arranged in the internal wall of the side pocket mandrel.