A reservoir assembly (20.50; 30.50) comprising: - a reservoir housing(20.1; 30.1), a piston (20.3; 30.3), and a locking plug (20.2; 30.2), both movably arranged inside the reservoir housing (20.1; 30.1); wherein the volume between the piston (20.3; 30.3) and the locking plug (20.2; 30.2) defines a reservoir cavity (20.5; 30.5); - a reservoir outlet (20.14; 30.14); and - a biased actuator (20.10; 30.10) configured to act on the piston (20.3; 30.3); - an interlock (20.6; 30.6) configured to prevent movement of at least one of the locking plug (20.2; 30.2) and the piston (20.3; 30.3); the interlock (20.6; 30.6.) having a locked position and an unlocked position, wherein - the locking plug (20.2; 30.2) is configured to be movable from a first position, when the interlock is in the locked position, to a second position, when the interlock is in the unlocked position, wherein in the first position the reservoir outlet (20.14; 30.14) is not in fluid communication with the reservoir cavity (20.5; 30.5) and in the second position the reservoir outlet (20.14; 30.14) is in fluid communication with the reservoir cavity (20.5; 30.5); and - wherein when the interlock (20.6; 30.6) is in the locked position the locking plug (20.2; 30.2) seals the reservoir outlet (20.14; 30.14), characterized in that, - when the interlock (20.6; 30.6) is in the unlocked position the locking plug (20.2; 30.2) is free to move and - comprising a fluid (20.8; 30.8) inside said reservoir cavity (20.5; 30.5), wherein, when the interlock (20.6; 30.6) is in an unlocked position, actuation of the piston (20.3; 30.3) by the actuator (20.10; 30.10) causes movement of the locking plug (20.2; 30.2), and - wherein the actor (20.10, 30.10) comprises a spring to exert a force onto the movable piston (20.3; 30.3). - a reservoir housing(20.1; 30.1), a piston (20.3; 30.3), and a locking plug (20.2; 30.2), both movably arranged inside the reservoir housing (20.1; 30.1); wherein the volume between the piston (20.3; 30.3) and the locking plug (20.2; 30.2) defines a reservoir cavity (20.5; 30.5); - a reservoir outlet (20.14; 30.14); and - a biased actuator (20.10; 30.10) configured to act on the piston (20.3; 30.3); - an interlock (20.6; 30.6) configured to prevent movement of at least one of the locking plug (20.2; 30.2) and the piston (20.3; 30.3); the interlock (20.6; 30.6.) having a locked position and an unlocked position, - the locking plug (20.2; 30.2) is configured to be movable from a first position, when the interlock is in the locked position, to a second position, when the interlock is in the unlocked position, wherein in the first position the reservoir outlet (20.14; 30.14) is not in fluid communication with the reservoir cavity (20.5; 30.5) and in the second position the reservoir outlet (20.14; 30.14) is in fluid communication with the reservoir cavity (20.5; 30.5); and - wherein when the interlock (20.6; 30.6) is in the locked position the locking plug (20.2; 30.2) seals the reservoir outlet (20.14; 30.14), characterized in that, - when the interlock (20.6; 30.6) is in the unlocked position the locking plug (20.2; 30.2) is free to move and - comprising a fluid (20.8; 30.8) inside said reservoir cavity (20.5; 30.5), wherein, when the interlock (20.6; 30.6) is in an unlocked position, actuation of the piston (20.3; 30.3) by the actuator (20.10; 30.10) causes movement of the locking plug (20.2; 30.2), and - wherein the actor (20.10, 30.10) comprises a spring to exert a force onto the movable piston (20.3; 30.3).