Siphon Effect in FM?

[sjohns4]

I was discussing a proposed PS & FM with a trusted pump rep recently and he through out this concept:

I'm pumping up a 300' mountain then down 200' on the other side. I did the preliminary design checking to make sure we'd gravity flow from the high point, then adding the friction loss from the uphill piping to the highpoint elevation. His concept was to only put an air release valve (not vacuum release) at the high point, make sure the pump could get the liquid over the top, but then add the friction loss in the whole pipe to the difference in elevation between the begining and ending point.

Basically he's suggusting using the siphon effect once the flow brakes over the top to design the pumps. I see where he's comming from on paper, but has anyone ever done this in practice?

Thanks,

Mike

 

[bimr]

The pumping scenario that you describe is done all the time.

You still need a vacuum release. The vacuum release can prevent a column separation from occuring. With a column separation, you may have water hammer:

http://www.win.tue.nl/analysis/reports/rana04-34.pdf

A large vacuum can also collapse the pipe.

 

[sjohns4]

I have always put a vacuum release at the high points for just that reason. However, if you have a vac release at the high point how would you take advantage of the reduced head from the siphon effect on the downhill side?

 

[bimr]

Maintain the pressure in the pipeline. You can use a backpressure valve on the discharge.

 

[PEorl]

Do you have to use the backpressure valve on the discharge?

 

[bimr]

Not necessarily. It depends on the discharge conditions.