siphon question

[eteagle]

I built a siphon over a dam - 4" schedule 35 about 100'. Inlet has float valve. Filled siphon from outlet with pump. Got good flow but highest section (top of dam) suffered a 4' total collapse of the sewer pipe. Why? How come pressure inside pipe at that spot is less than atmospheric?

Thanks

Ernie

 

[WVBill]

Did the float valve on the inlet close or get clogged? If so, the head of water on the outlet side would pull a "vacuum" behind it as if flowed out - until the "vacuum" equalled the weight of water in the pipe (minus atmospheric pressure).
Depending on the amount of fall, that vacuum could colapse your pipe.

 

[leaddog]

I used a siphon on my dam several years ago with 4 in sewer pipe. you can't have a float valve on the inlet as pressure on the outlet end will be GREAT. Depending on how much fall you have. Also do't get to close to the inlet end when it is flowing as the suchion is great and you or some clothing could get caught and you could drowned. Remember the girl that got her hair in the suckion trap in a hottub and she couldn't get loose and drowned a couple of years ago.
I had a turtle get caught and it stopped my siphon.
leaddog

 

[eteagle]

Thanks

I used a float valve in order to fill the pipe. Its about 100' long. I kept getting air locks (big ones) until I filled the pipe from the outlet end. Do you think I can fill it this way if I remove the float valve?

Ernie

 

[leaddog]

The way I started mine was easy as the water level was only about 18in from the top of the dam. I just held the pipe up at both ends and filled it and when it was full dropped both ends at the same time. then I added more pipe on as I needed to get it lower.
It was almost empty and I had stopped the siphon and we got a 2in rain and I got 5 ft of water in over nite. To start it up again I had to use a plug on both ends and I held one end and my dad held the other. MY wife filled the pipe thru a hole in the top and when she got it full and closed off she yelled and we both pulled the plugs. You have to pull the intake a split second first or else the sucion will not let you pull it. We had 140ft of 4in pipe to fill and it took a long time. Had to do it twice because that is when the turtle got caught and stopped it. But it drained a 7 acre lake 14ft deep in less than 6 wks even with the springs flowing. Alot of water will flow out of a 4in pipe with 20ft of head.