A pump for an oral irrigator includes a pump chassis, an eccentric end plate movably connected to the pump chassis, a first alignment shaft connected to the pump chassis, a second alignment shaft connected to the eccentric end plate, a first gear rotating around a longitudinal axis of the first alignment shaft, and a second gear engaging the first gear and rotating around a longitudinal axis of the second alignment shaft. By selectively moving the eccentric end plate relative to the pump chassis selectively moves the second gear relative to the first gear.