Construction details: The inner-diameter of the watertube is 4 mm. The ballneedle entry inside the watertube is in a height of 12 – 17 cm above the water-entry. In these 12 – 17 cm from bottom to ballneedle-entry i reduce the inner diameter of the watertube to 1 mm. The air-pressure is very low. The lifting of waterbubbles is very slow. The system is a very silent one.