Siphon - Requirement for Submerged Discharge? 1

[GrahamC001]

Colleagues,

I am designing a pipe siphon to effect the drawdown of a reservoir under emergency conditions. To give a sense of scale I've done a preliminary sizing at 0.5m dia.

I've struggled to find any good guidance on the design of this type of installation (there seems to be plently out there on self priming and air regulated siphons, but less on the basic 'pipe over an embankment' type).

Much of the guidance I have managed to find suggests that the downstream end needs to be submerged. This is going to be difficult in the situation I am designing for (discharge half way down the existing spillway) so my question is - why? If this is for priming, can I get away from needing it by having a valve at the downstream end which is closed during priming?

I'd also be grateful for any suggestions on a source of good design guidence on this type of siphon.

Thanks,
Graham

 

[MiketheEngineer]

Do not have much design info - just practical ideas. The "downside" definitely needs to be lower than the "upside" - the more the better. Never heard that it needed to be submerged - although that may slow the output a bit and not allow an air bubble burp to enter the pipe and possibley break the siphon. Just put it in a pail at the exhaust end.

When we were kids - we used to scavenge every hose we could find in the neighborhood in order to siphon our neighbors pool - so we could clean it, paint it and THEN SWIM!! We would fill the hose with one kid on each end holding it closed. Then we would yell to each other and get the siphon going. It would run for days - worked great.

 

[bimr]

The discharge end may need to be submerged in order to start the siphon. However it is not necessary to have a submerged disharge.

See page 11.3.7 Siphons:

http://evidence.environment-agency.gov.uk/FCERM/en/FluvialDesignGuide/Chapter11.aspx?pagenum=3

A stilling basin is probably necessary on the discharge side to ameliorate other problems such as turbulence and erosion.

The valve that you selected may be used instead of a submerged discharge. Note that the vale may collect debris and plug with debris. The valve may be a freezing issue as well.

http://www.eng-tips.com/viewthread.cfm?qid=165827&page=30

 

[beej67]

I've seen siphon outlet control structures with a "turn-up" at the end. I presume the turn-up serves the same function as having the end submerged.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[cvg]

submerging the end reduces the possibility of air getting in the pipe but is certainly not necessary.

http://en.wikipedia.org/wiki/Siphon

 

[msquared48]

I have use a small (1" dia) siphon to empty my swim spa and hot tub to clean them for years, never submerging the outlet.

The only time I have found where air will travel up the hose and break the siphon action is when the flow is reduced due to a lowering of the available head, or when the flow is restricted due to an obstruction in the line. Otherwise, it's just fine.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask