A needle assembly having a build-in valve, comprising: - A hub carrying means for connecting the hub to an injection device, - A proximal cannula part for penetrating into a reservoir containing a liquid drug, - A distal cannula part having a distal tip for penetrating the skin of an object, - A telescopically movable shield which is movable relatively to the hub between: - a first position wherein the shield axially covers the distal tip of the distal cannula part, and - a second position wherein the shield is axially retracted proximally to the distal tip of the distal cannula part, - A valve positioned between the proximal cannula part and the distal cannula part and which valve is closed when the telescopically movable shield is in the first position and open when the telescopically movable shield is in the second position, characterized in that, the needle assembly is multiple usable such that the same distal needle cannula part is used for several injections, and the telescopically movable shield carries a reservoir in which the distal tip of the distal cannula part is maintained and cleaned during injection, and wherein the valve is opened when the telescopically movable shield has been retracted a specific distance proximally to the distal tip of the distal cannula part, wherein the distal cannula part and the proximal cannula part form ends of one uniform needle cannula, which needle cannula comprises a distal radial opening and a proximal radial opening; where the distal radial opening connects to a distal lumen, and the proximal radial opening connects to a proximal lumen, and which two lumens (17, 18) are separated by a lumen blocking part, and wherein the telescopically movable shield further comprises means for generating a liquid passage-way from the proximal radial opening to the distal radial opening when slided axially such that the liquid drug can flow from the proximal lumen and into the distal lumen. - A hub carrying means for connecting the hub to an injection device, - A proximal cannula part for penetrating into a reservoir containing a liquid drug, - A distal cannula part having a distal tip for penetrating the skin of an object, - A telescopically movable shield which is movable relatively to the hub between: - a first position wherein the shield axially covers the distal tip of the distal cannula part, and - a second position wherein the shield is axially retracted proximally to the distal tip of the distal cannula part, - A valve positioned between the proximal cannula part and the distal cannula part and which valve is closed when the telescopically movable shield is in the first position and open when the telescopically movable shield is in the second position, characterized in that, the needle assembly is multiple usable such that the same distal needle cannula part is used for several injections, and the telescopically movable shield carries a reservoir in which the distal tip of the distal cannula part is maintained and cleaned during injection, and wherein the valve is opened when the telescopically movable shield has been retracted a specific distance proximally to the distal tip of the distal cannula part, wherein the distal cannula part and the proximal cannula part form ends of one uniform needle cannula, which needle cannula comprises a distal radial opening and a proximal radial opening; where the distal radial opening connects to a distal lumen, and the proximal radial opening connects to a proximal lumen, and which two lumens (17, 18) are separated by a lumen blocking part, and wherein the telescopically movable shield further comprises means for generating a liquid passage-way from the proximal radial opening to the distal radial opening when slided axially such that the liquid drug can flow from the proximal lumen and into the distal lumen. - a first position wherein the shield axially covers the distal tip of the distal cannula part, and - a second position wherein the shield is axially retracted proximally to the distal tip of the distal cannula part, - A valve positioned between the proximal cannula part and the distal cannula part and which valve is closed when the telescopically movable shield is in the first position and open when the telescopically movable shield is in the second position,