Siphon Drawdown Pipe Line

[QFlow]

HELP! Does anyone know of any examples for a siphon design? My project consists of a pond that requires drawdown via a siphon pipe line. Looking at flows=12,000 GPM and pipe diameter of 24" or better. Head is approx. 15 feet. Pipe line length=1000 feet prior to high point and 100 feet downstream of high point.

Thank you.

 

[GeoPaveTraffic]

There's not much to it, just place your pipe with a T or cleanout at the high point. The trick is then to fill the complete pipe with water getting all of the air out. Then unplug the pipe and the siphon will start. If you don't get all of the air out or don't remove the up and down stream plugs at the same time, the water will just drain out and the siphon will not start. In that case just try again.

 

[jfp10130]

A 12,000 gpm does have several special considerations, due to its size alone. The "plugs" mentioned by GeoPaveTraffic will have over 3,000 lbs of force on them. Once the siphon is filled through the high point, the plug or valve in the lake can be removed without worrying about column separation. The downstream plug (or preferrably a valve in this size) can then be opened partially or fully. Without the valve, you have to open the fill port to break the siphon, which may be difficult depending on the pressure differential across the cap (atmospheric outside and less inside). Will 12,000 gpm lead to rapid drawdown slope failure of the dam? Is 15 feet the elevation difference between the lake surface and the discharge of the siphon pipe? How much elev difference is there between the high point and the lake?

 

[QFlow]

jfp10130: yes, 15-feet is the elevation difference between pond surface and discharge. highpoint to pond surface is approx. 6-feet. An evacuation valve will be placed at highpoint with a valve on the downstream side, for closure and possible throttle. my biggest concern is that the suction side, prior to high point, being much longer (900-ft) than the discharge side (25-ft), after hight point, may cause slug of water to break away at high point since there may not be enough gravity (or weight) to pull a continuous "string" of water through pipe. I do, however, have the needed static head and head to overcome frictional losses.