A device close to the body for an infusion system for delivery of an infusion fluid from a container, bag or the like, through a tubing to a user location (human being or animal) via a veinflon/cannula, and means to maintain the pressure in the bag so that the fluid flows through the tubing to the user location is described. The device is characterised in that the tubing comprises a reduction valve for automatic regulation of the fluid pressure to within a desired range and said desired pressure is maintained as long as there is fluid in the bag. A preferred application of the device is also described. Furthermore, the invention relates to a new construction of a box for storage of the bag during the delivery of fluid to the patient, and also a new construction for a reduction valve.