I built a new dam and put in a siphon system with 8 inch drain pipe. The water rose above the level of the top of the pipe onto the overflow pipe, but the water in the siphon system just flowed at about 1/4 flow. I closed the downstream side and filled the pipe and then closed the vent - no siphon - just the quarter flow. I concluded that I had a blockage on the water side, so I drained the pond (by other means). I found no blockage. I dug up the 8 inch pipe - no breakage or disconnect. I'm at my wits end! Any more ideas?

Thanks

Ren,

Welcome to the forum! Sorry to hear your siphon is not working as intended. Can you give us a rough drawing of exactly how it is laid out and was put together. Siphon systems are very simple, but must be 100% sealed and installed correctly to function. Air leaks are the usual problem, especially on the dam side.

Even without the shipon not kicking in you should get more than 1/4 flow though the pipe. How much lower is the pipe at the back of the dam compared to the front?

Do you have a line at the top of the inlet that lets out air until the water level reaches the top of the outflow pipe? You may have an air lock.

Thank you for the question!

Indeed, I do have a 4 inch vent on the top of the pipe. When the water is overflowing - even the spillway, the 8 inch pipe - with the 4 inch vent open, still flows at about 2 or 3 inches deep.

The non-water side of the dam is about 20 feet longer and about 7 feet more in elevation.

Thanks

Are you saying the non-water side outlet is higher than the water side? If so there is an issue

No,
I stated it poorly. Actually, the non-water side is about 85 feet long as opposed to 45 on the water side, and the drop is probably more than 10 feet - more on the non-water side

I'm not sure how to send a drawing, but I did go to the pond and make some measurements. The dam wide (water side) is made up of 4 sections of 8 inch locking drain pipe - green in color. The total length of the pipe on the dam side is 47 feet. There is a 22.5 degree ell 10 feet from the water (flattening the slope for the suction), and there is a 22.5 ell at the top on the dam. The ell at the top goes to a tee with a 4 inch outlet on top. The standpipe for the vent has a plug that I can screw on and off.

Across the dam is about 19 feet, and then it drops off 85 feet on the non-water side. I was surprised that it was that far!

Just for grins, I took two golf balls with me. The first I stuck into the pipe on the water side. I had to toss it foward because of the slope toward the non-water side. It quickly shot out of the pipe into the small amount of water that is in the pond. To be sure that I had the ell at the high point with some slope across the dam, I set the other ball stationary, and it rolled slowly away and soon shot out of the pipe at the bottom.

I hope this helps you picture the dam site and the siphon. If not, I'll make a picture and figure out how to post it.

Thanks,
REN

Are you sure you got the air out. We use a vent.

Thanks for the suggestion.

I did not pull a vacuum on it, but, on two occasions, the water level was well up on the 4 inch pipe - completely over the top of the 8 inch pipe - and the 8 inch pipe was flowing only about 3 inches deep. I simply don't understand how that could be.

Also, with the water level above the 8 inch pipe, I put a cap on the outlet and filled the pipe. I then closed the vent and released the plug - the pipe enptied and it went back to the 4 inch flow.

REN

We recently had a siphon pipe that air locked. We had to drill a small hole right behind the vent tube to get it to start siphoning. You could possibly not have the vent tube set properly in length.

I had the same problem at first, and I am sure this is your problem. Try putting a 45 degree elbow at the end of the pipe, pointed up. If you don't have a 45, use a 90. What is happening is the water is sliding down the pipe so fast it never creates the air lock, and therefore the suction needed to start the siphon. In other words, air is entering the end of the pipe and going back up. The elbow will keep this from happening.

Look at this thread

I posted this when I found the problem with my siphon.