A flow regulator for low fluid flows, comprising: - an inner non-revolving core element; - an outer housing, having a hollow base section and being revolvably supported co-axially with said core element; - first and second chambers (14; 16) disposed between said core element and said outer housing, each chamber (14; 16) having an inlet and an outlet (38; 42), said outlet of said first chamber and said inlet of said second chamber being connected by a flow restriction path; - an at least partly elastic diaphragm separating the two chambers (14; 16) and sealing an inlet to a discharge tube when pressure at said first chamber is higher than pressure in said second chamber, said diaphragm comprising an outer ring, a central disk, and a flexible intermediate section connecting said outer ring to said central disk; and - a circular spring placed in the second chamber below said diaphragm and around said discharge tube; and - said inlet to the discharge tube being connected to said outlet of said second chamber when said central disk is spaced apart from said inlet to the discharging tube, and having a lower outlet connectable for infusion to a patient; characterized in that it further comprises: a graduated flow-rate locking ring housing a disk-like body and a locking sleeve disposed between the outlet of said discharge tube and said base portion of said outer housing, and a lock key, wherein said lock key is adapted to be in a low position or in an upper position, wherein said locking ring is adapted to be in an open position or in a secured position, wherein said locking sleeve is adapted to be pushed up to a locked position, wherein when said locking ring is in its open position said lock key is in a low position freeing said outer housing to be revolved to any position within its range including a priming position while said locking ring can be revolved to select any flow-rate within the regulator range, whereas when said locking ring is in its secured position said lock key is raised to its upper position and said locking sleeve is restricted to the regulating and closed positions and said locking ring is secured at the selected flow rate, whereas when said ring is pulled down again from the secured position to said open position it can be re-revolved to re-select any flow-rate within the regulator range while said lock key remains in its locked position, whereas when said locking sleeve is pushed up to its locked position once said ring is situated in its secured position the ring is permanently locked at the selected flow rate. - an inner non-revolving core element; - an outer housing, having a hollow base section and being revolvably supported co-axially with said core element; - first and second chambers (14; 16) disposed between said core element and said outer housing, each chamber (14; 16) having an inlet and an outlet (38; 42), said outlet of said first chamber and said inlet of said second chamber being connected by a flow restriction path; - an at least partly elastic diaphragm separating the two chambers (14; 16) and sealing an inlet to a discharge tube when pressure at said first chamber is higher than pressure in said second chamber, said diaphragm comprising an outer ring, a central disk, and a flexible intermediate section connecting said outer ring to said central disk; and - a circular spring placed in the second chamber below said diaphragm and around said discharge tube; and - said inlet to the discharge tube being connected to said outlet of said second chamber when said central disk is spaced apart from said inlet to the discharging tube, and having a lower outlet connectable for infusion to a patient; characterized in that it further comprises: a graduated flow-rate locking ring housing a disk-like body and a locking sleeve disposed between the outlet of said discharge tube and said base portion of said outer housing, and