The fluid-flow device (100) of the invention comprises a stack (30) covered by a closure wafer (20), said stack (30) comprising a support wafer (36), a layer of insulating material (34), and a silicon layer (32). The closure wafer (20) and/or said silicon layer (32) are machined so as to define a cavity (38) between said closure wafer (20) and said silicon layer (32), said support wafer (36) has at least one duct (102) passing right through it, said layer of insulating material (34) presenting at least one zone (35) that is entirely free of material placed at least in line with said duct (102) so as to co-operate with said cavity (38) to define a moving member (40) in said silicon layer (32), the moving member being suitable under the pressure of liquid in said cavity (38) for reversibly moving towards said support wafer (36) until contact is made between said moving member (40) and said support wafer (36).