Unless your pool level is above the top of your siphon tube's highest point AND the vent tube is under water, a siphon will not start without manually filling the outlet pipe.
This morning I started my siphon without the pipe totally submerged and without filling the pipe.
1) Lake level was about 2/3 of the way to the top of the 6" pipe.
2) I put a 3" PVC cap over the end of the vent pipe because the vent pipe was a couple of inches above the water's surface.
3) Siphon did not start automatically and a flat ribbon of water was shooting out of the end of the pipe and going about 3 feet.
4) Looking in the outlet I could see the elbow wasn't sealed and the flow wasn't changing from drain to siphon.
5) I placed both hands over the end of the 6" outlet pipe to slow/stop the water and keep it inside the outlet and form a water seal.
6) Once the outlet was sealed, things started happening.
7) There were several gentle surges and the volume of water increased with each one.
8) About 2 minutes later the siphon was at full flow and the torrent of water was now being shot about 10 feet downrange.
I'll shut it off and do this all again tomorrow with pictures to make it all clearer.
Without the elbow, often a siphon will never even start and reamins as only a simple overflow pipe with gravity flow.
I agree 100%. The elbow is there to seal the outlet and allow a siphon to start. No seal..... No siphon start.
BTW...what is wrong with your current outlet that needs fixing?
My outlet only seals when there is just a trickle of water coming down the pipe. As the volume, and velocity, increase as the lake level increases, the very small pool of sealing water is carried out of the pipe by the force of the rapidly moving water coming down the pipe. The problem is that there's not enough volume of water to resist the high energy water coming down the pipe. As soon as the pool of sealing water is gone, air enters from the bottom and no siphon can begin. When I capped off the end of the pipe with my hands, even though the pipe was not totally sealed off, I was able to keep the elbow full and the seal intact. With the intact seal and the vent pipe capped off, it only took a minute or two and the siphon was going.
In short, if I can't keep the outlet sealed and keep the air from getting into the pipe, the siphon won't start. Once the seal is restored, the flow quickly changes from drain to siphon.
I'll try to video this tomorrow and will post it on youtube.
-RFL
