With an atmospheric air pressure of 1 bar, this ambient pressure can thus push a maximum water column of 10 meters upwards. After all, the maximum negative pressure that can be generated is a vacuum. The illustrated example with the bottle also clearly shows that the maximum height be overcome between the higher water level and the apex of the hose is limited by the maximum suction lift of about 10 meters. Finally one obtains in this way a single tube, which sucks the water from a higher level over the apex and then drains it into a lower level. The last step is to use another flexible tube instead of the bottle. The pressure gradient required to pump the water will then form directly inside the water. And finally, even an initial air volume can be completely dispensed with. In principle, the air volume in the bottle at the beginning can be chosen arbitrarily small. The water is sucked in so to speak by the negative pressure in the bottle, which is produced by the outflow of the water. This tube is now placed in the vessel from which the water is to be sucked off. Only a second flexible tube has to be attached to the bottle from above. The resulting negative pressure in the bottle can then be used to suck water from another vessel. Figure: Demonstration of the siphon-spillway-principle Since no air can inflow through the relatively small hose, a negative pressure is created inside the bottle. The outflow of the water leads to an increase in the volume of air inside the bottle. If the bottle is now turned upside down, the water will begin to flow out through the tube. A flexible tube is mounted on the screw cap of the bottle. In order to better understand this, a plastic bottle filled with water is first considered. This paradoxical behavior is due to hydrostatic pressure. Figure: Draining a pool with a garden hose Explanation Such an arrangement is also called a siphon or siphon spillway. As long as the lower end is always held lower than the water level, the water is also carried over larger heights, such as over the edge of the pool (to the maximum height to be overcome later more). Once the water is sucked in, it runs out of the hose permanently. The outside end of the hose only has to be lower than the water level. If, for example, you want to empty a pool by a garden hose, you only have to place one end of the hose over the edge into the pool and the other end outside.

Syphoner demo