Siphon flow sizing
Siphon flow sizing
(OP)
We are trying to design a smaller reservoir siphon to replace a 12" ID siphon that flows much higher than is desired on this site. The siphon works well and is HDPE fusion pipe and we intend to use the same design and material that currently works but in a smaller pipe size but am not sure I am calculating the projected flow right for 6" and 8" inside diameter HDPE. The inflow elevation to the high water line is 10 feet and inflow pipe length to center of dam (highest point) is 83 feet. the discharge is 28 feet below the high water line and the length of discharge from highpoint at dam center is 102 feet to the gate valve. There is then 20 feet of pipe past the gate valve for a total pipe length 205 feet. I am struggling to calculate the flow on the 6" and 8" pipe sizes. Can anyone help? Thanks





RE: Siphon flow sizing
RE: Siphon flow sizing
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Siphon flow sizing
RE: Siphon flow sizing
RE: Siphon flow sizing
First off, in HDPE speak 12", 8" and 6" don't exist. You have at a guess 315mm, 250 and 180mm
For the 180mm pipe with say 150mm bore, you get about 80 litres per second at about 4.5 m/sec.
The 250 mm, say 210mm ID, you get about 240 litres/sec at nearly 5m/sec.
Your 315 ( 280mmID) probably gives you about 350 -400 l/sec
So 3-5 cfs (cubic feet per second?) = 80 litres/sec to 135 l/sec.
So the 180mm pipe will probably do it, especially if you choose a relatively high SDR as my graph ran out at a pressure drop of 10:100 and you have 14:100.
If you're having trouble maintaining syphon in your 315 pipe, then you're either not clearing the pipe properly once the flow starts, you're sucking in air at the entrance or there is a leak somewhere. So long as you keep your exit pipe full of liquid, reduced veleocity shouldn't make a difference, but clearly you're getting air in somewhere then you don't have the velocity to clear the air out - usually about 1- 1.5 m/sec.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Siphon flow sizing
RE: Siphon flow sizing
For the 8-Inch HDPE, 1.9 to 3.2 CFS.
For the 6-Inch HDPE, 1.0 to 1.65 CFS.
RE: Siphon flow sizing
RE: Siphon flow sizing
A better method is to use the pressure drop across the siphon pipe, estimated at 0.3 to 0.7 psi with plastic pipe when flowing at 3-5 cfs.
For the 12-Inch HDPE 3 to 5 CFS.
For the 8-Inch HDPE, 1.8 to 2.8 CFS.
For the 6-Inch HDPE, 0.7 to 1.15 CFS.
These flow give the same pressure drop across the 205 feet of pipe.
There are online calculators that may be used to determine the headloss:
http://irrigation.wsu.edu/Content/Calculators/Gene...
RE: Siphon flow sizing