Pond Boss Forums POND CONSTRUCTION Building a dam Siphon not working

I've been studying auto syphons as I am currently installing one. One thing I know from irrigation pump priming is it is hard to know where or if you have a leak. I would try priming the air vent from the top with the smaller ball valve closed. If this doesn't stay as water you have an air vent leak. At your current water level this should remove your air vent from the equation and it should close to full syphon. I've used a temporary syphon a lot to pull down a pond. I've had the temporary one stop for apparently no reason. Upon closer inspection, I could here some air leaking into one of the gaskets and tightening them kept the syphon working. My point is any amount of air leak could cause it not to work. Could you have a crack or tiny leak at any exposed joints? Maybe use shaving cream on the exterior to see. I've done this on irrigation lines.

Is some water coming out of the syphon? Your water level is above the top of the main pipe, syphoning or not, some water should be coming out.

I'm in the process of gluing my air vents on my new syphon. I am using Tpost to support the weight (Those ball valves weigh a lot). Your air vent doesn't have a long run but it isn't supported and anything could bump it and damage the joint. Just an observation as I am doing this myself. My air vent is 2" btw.