Using a siphon to transfer water along a dike out of a reservoir is an extremely economical water intake method. However, because the pressure at the top of the siphon is less than atmospheric pressure, air released from the water collects at the top. The accumulation of air reduces the pipeline’s capacity to transport water. In the worst case scenario, the water flow in the siphon stops completely. Therefore, a new automatic air evacuation system to remove air from the siphon pipe that does not use the safety flow pump was developed.
In pipeline systems connected with 5 irrigation reservoirs in the M irrigation project of Okinawa Prefecture, siphon pipe systems equipped with automatic air evacuation were used. Through the use of this system, the pressure in the long distance siphon pipes decreased, and as a result, the system was unable to maintain a consistent flow. Measurement instruments including a pressure gauge and a flow meter installed in the system verified hydraulic performance in long distance pipes that were using automatic air evacuation. The results revealed that when the equipment was operating normally, the siphon flow formed temporarily, but over time the siphon flow degraded and finally ceased. It is hypothesized that the cause of this is related to the longitudinal profile design of the long distance pipes. Important points to consider in the design of future siphon pipe systems that are equipped with automatic air evacuation are discussed.
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