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### Siphon Flow Rate Equation and Calculator

Siphon Flow Rate from Small Pipes Equation and Calculator.

The effective (differential) head, Δh, over the pipe or siphon has to be measured as accurately as possible, but the installation also has to be practical. For field measurements a transparent hose acting as a siphon, as illustrated below, will be found useful. By keeping the hose in a vertical position Δh can be read from a scale. Since siphon fluid source level will drop as soon as the device is installed, a meter may be placed and read quickly to obtain a reasonably accurate Δh-value.

From a hydraulical viewpoint, two types of pipes (or siphons) can be distinguished:
- ‘small diameter pipe’, being a pipe with a .length L considerably more than D,
- ‘large diameter pipe’, which has a relatively short length of 6 Dp ≤ L ≤ 20 Dp,.

Related:

Siphon Flow and Discharge Rates Tables and Charts

Siphon Flow Rate:

For ‘small diameter pipes’ friction losses in the pipe play a significant role and the head loss coefficient is estimated to equal:

Symbols used:

Q = Discharge (m3/s)
Dp = Siphon internal diameter (m)
g = Acceleration due to gravity (9.81 m/s2)
Δh = operating head (m) Note: That head height will change when siphoning from a fixed volume.
f = friction loss coefficient (0.019)
L = Siphon length (m)
ε = Friction losses (dimensionless)

Discharge Measurement Structures
Third Edition
M.G. Bos
International Institute for Land Reclamation and Improvement / ILRI

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