So as a spin-off from my overfilled pond. Landowner and I went down yesterday to build a siphon. Using 4” pvc pipe we put a 90 on the intake end and covered it with wire mesh. Weighed it down with a cinder block and dropped it down. It’s probably 4ft under water. We came up the bank with a 45 and connected more 4” pipe, put in a T joint, then another length of pipe, a connector, then another 45 for the backside of the dam. Attached another 10ft of pvc and a screw cap at the end of the outflow pipe. The backside is really steep and the outflow end is way below the water level and the intake end. Ok all good so far.

The problem started when we tried to fill the pipe at the T. We ran 100ft of hose from the cabin and it ran wide open for 45 minutes and never could fill the pipe. We could hear water swirling in the pipe where it met the pond. So all we were doing was putting more water in the pond…. If we lifted the section of pipe that was exiting the pond (with the intake 90 on the end) the T would burp air and and the pipe would fill. We screwed one the cap at the T and attempted to see if it would work. I went down the backside of the dam and unscrewed the end cap. As expected, all the water in the pipe drained but no vacuum was created and it stopped. By this time it was 8pm and we called it.

Somehow water is flowing into the pond when we try to fill it at the T but I can’t figure how. I would think the water would enter the intake end and force air out and fill the pipe until it was level with the water surface. I’ve got to figure a way to get the pipe to fill. Any ideas are welcome.

Try capping the outfall end, filling the pipe at the T, capping the T, then uncapping the outfall end to see if that’ll create a vacuum.

Going to have to push the hose from the T until its a very downward slope to the exit point. Probably have to burp it at some point to let air out.

If I am understanding you correctly, you didn’t put a backflow preventer on the pond side?

I would put a backflow preventer on the pond side, and a valve on the outflow side. Fill up with water, open the valve. Should flow and open the backflow preventer and start to drain.

Edited to add… cap the tee after filling it up and before opening the outflow.

You got to keep the water from flowing back to the pond and the sure way to do that is a backflow preventer.

Do they make a back flow preventer for a 4” pipe? I’ve seen the ball valve thing but don’t know if that will work. If I open the ball valve I’m worried that all the water in the pipe will run back into the pond.

That’s precisely what we did. Epic fail.

This was posted in the other thread. You have to put a check valve on the pond side so water can only flow one way. The one in the video looks like a 4” to me.

https://www.youtube.com/watch?v=ZUsTT_RUEdQ

I would have just put a pump on the outflow to get the siphon started. Just pour buckets of pond water in the tee and no messing around with a hose.

I have an 8" siphon system on a 5 acre pond and it siphons every time the water gets high enough. I'm not sure I completely understand how you set yours up, but it seems like the biggest difference is that we dug through the dam to get the horizontal pipe at water level, while it sounds like you laid it on top of the dam. Is that correct? So you are trying to make the water first go up to the top of the dam? It might be possible to make that work, but all the permanent systems I've seen have the horizontal pipe at the water level. I think your guy will have to build a system like this eventually; might as well go ahead and do it.

My father and I installed ours entirely by hand, but a backhoe will make it an easy job. Good luck getting it done.

Check valve and backflow preventer serve the same purpose. This is what you need. Yes they make them in 4”

You need a check valve on the pond side. Probably can't get that locally.

That sounds more like a drain pipe. No siphon is involved correct? Basically just an overflow pipe I’m guessing?

This won’t work without a check valve on the pond side. The pipe will never fill. It will just flow into the pond.

It’s like siphoning gas. You have to keep the gas from flowing back into the tank. You use your mouth to keep that from happening when stealing gas, a check valve will keep it from happening in this situation.

You don’t have to have a check valve. Cap the outflow pipe and fill up the pipe on the backside of dam. Then close the T off and uncap the outflow. Need to have at least 2-3 times length of pipe on backside than amount of pipe in pond

This would work with enough pipe on the down hill side. Just have to have enough to pull the water up and across the damn. The grade would have to be enough to create enough head pressure to pull the water up the pond side. I assumed since it didn’t work when they tried it, they didn’t have enough head pressure

Exactly. This is how we install and use them at Southeastern Pond Management. Never have used a check valve. But you gotta have enough “pull” to get it started. If you don’t have a “breather” pipe on it. Once it gets down to where you want it, open the T to let air in and stop it

As stated above, you need more pipe or more drop on the outfall side.

No check valve needed. As described above works perfectly.
One thing I didn’t see mentioned is to slightly slope the “horizontal” portion that’s across the top of the dam toward the back of the dam. This will ensure water flows to the back of the system and not out the pond side when you’re filling it.

As said the key to making it work is length of pipe on back side. The more elevation difference the better.

We have a real steep backside of the dam. May need to add another 10 feet tho.