An electro-valve for discharging a common rail while maintaining a minimum pressure, comprising an electro-magnetic coil inside which is arranged a movable plunger, controlling the displacements of a movable axis engaging a ball valve, said movable plunger being urged in the closing position of the ball valve by a spring housed inside a bearing cap, wherein a bottom wall of the bearing cap surrounds an external surface of the movable plunger, wherein a clearance between the external surface of the plunger and an internal wall of the bearing cap is filled with a film of fuel, the opening movement of the plunger causing the fuel to flow from a room situated on top of the plunger to a bore in which the axis is arranged, wherein a sleeve of a controlled thickness is arranged around the plunger within the clearance to set the thickness of said film of fuel.