Water siphon question 2

[FireMed]

Hello.
I am trying to figure out how to calculate the drop needed to siphon water a total of 600 meters (2000+ ft) to overcome a rise of 10m (33') in a 1.5" pipe.
The line will climb for 500m then drop for the last 100.
How far down do I need for steady flow (no gushing)?

Any thoughts?
Thanks

 

[georgeverghese]

If there is a net rise of 10m, your siphon wont work. Else pls sketch this out.

 

[pierreick]

Hi,
Consider this document to support your work, you will find tips.
A sketch will help .
Pierre

 

[pierreick]

Hi,
Another resource.
Pierre

 

[LittleInch]

Agree with George. The practical limit for a syphon from water level to top of the syphon is about 8m.

Even if you get this, that a long way to get any flow with only 1 m or so differential l head, so your max height is really only about 5m in order to generate any differential head to get any flow.

Sectional drawing needed.

 

[FireMed]

Sorry for the delay.
Here is a drawing of the pipeline.

 

[Snickster]

As others indicated 32 ft is approximately the maximum lift possible under no flow static conditions. When flow is developed this will decrease the maximum lift somewhat and you might even loose the siphon effect. A hydraulic analysis is required to determine the actual maximum lift and flowrate possible. I would limit the lift to 8 meters (26 ft.) as a maximum as previously suggested

 

[FireMed]

Thanks for all the input into my questions. I appreciate all your time and resources you have forwarded.
I thought this may be a really long run with not enough drop for what I was trying to do. I may look at putting a solar pump on the feed end and running it that way, while the drop may help the water along.
Snickster, you mentioned a hydraulic analysis. Is this a formula or how is it done?

Thanks all

 

[Doug Hunter]

Yes, your best bet is a pump. You only need a 1" drop to keep the siphon running. But starting it would be the challenge. Bernoulli's law tells us that we can only "suck" up a certain height (I think the 32 ft previously mentioned). One siphon option could be to cap the 875 m end, fill your pipe with the pond end at an elevation of 892 m, cap it, then drop it into the pond and uncap both ends. That would be very difficult. You could possibly pull it off by tee-ing in a temporary pump with some ball valves at the pond end to fill the 1000 ft long pipe section, then it could be charged to run on its own.

 

[georgeverghese]

From the photo, you have a net drop of 8m from inlet to exit. At first glance, that appears doable with a siphon type arrangement, but then you have a 17m drop from the top of the hill to final exit. With a total friction drop of say 2bar over 2000ft, the pump at inlet will need to develop some 1.4barg at inlet in order to keep pressure at high point at say 0.5bar abs as a minimum. Stop valve at exit to be closed on initial fill of this entire line. Roughly. 1inch vent valve at highest point on this line.

 

[katmar]

Is it possible to avoid the high point by following the contours from the source to the destination? If you bring the highest point down to around 890 m by making the line a bit longer you could make it work.

 

[LittleInch]

Sorry for the delay.
Here is a drawing of the pipeline.

Yup, agree with that above. A 9m elevation difference from water level to the high point is too much to create a working syphon.

To use a pump you really need to maintain a backpressure at the far end to avoid two phase flow and lots of slugging and intermittent flow.

So your pump needs to be capable of at least 15m diff head to ,keep a positive pressure at the high point.

You can operate in what is called slack flow where because of the height difference between your high point and end if the end is just an open pipe then even if you manage to fill it it will promptly empty at the high point down to a near vacuum. That will increase flow a bit up the slope, but then starts slugging and gurgling and spitting out the far end. If that's OK with you then go for it.

 

[georgeverghese]

For variable flow through this line, replace that stop valve at the end with a control valve and PIC sensing abs pressure at the high point to keep it above 0.5bar abs