There is disclosed a mechanical-vibration-generating-device for generating a mechanical vibration, the mechanical vibration having a vibration direction. The mechanical-vibration-generating-device comprises: rigid bushings comprising at least a beginning rigid bushing and a end rigid bushing, at least one axial piezoelectric stack positioned between the beginning rigid bushing and the end rigid bushing, the at least one axial piezoelectric stack having an imaginary axis; the imaginary axis being aligned with the vibration direction, a coupling for interconnecting the beginning rigid bushing and the end rigid bushing, a common internal channel defined in the rigid bushings and the piezoelectric stack, the first connective passage and the second connective passage defined in the rigid bushings providing a fluid path between the common internal channel and an ambient environment, the first connective passage having a first valve and the second connective passage having a second valve, the first valve being configured as an inlet valve and the second valve being configured as an outlet valve.