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4 Pipe Networks
Analysis
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7 Water Distribution System: Pipe Network Analyses
A water supply distribution system consists of complex network
of interconnected pipes,
service reservoir and
pumps
Water demand is highly variable, by day and season.
The distribution system must include: storage element
capable of flexible operation
water pressures within the system are maintained between 20 to
70 m
Pipe network analysis involves determination of the pipe flow
rates
and pressure heads 2 standard methods are generally used to
analyze pipe networks;
the loop method (Hardy-Cross method) and
the nodal method
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7.1 The Loop Method (The headbalance method)
Prof. Hardy-Cross (1936), often referred to as the Hardy-Cross
method.
Applicable to closed-loop network.
The basis of the method is as follows:
1. Flows in each pipe is estimated. At each junction, theseflows
must satisfy the continuity criterion.
2. Calculate the head loss for each pipe
3. If the HL = 0, then the solution is correct (the sign
convention is that clockwise flows are positive).4. If not,
apply a correction factor Q to all the dischargesin the loop and
return to (2).
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Q for rapid convergence is given by:
(35)
Figure 11 Flow in pipe loop
ifi
fi
Qh
hQ
/2
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Example 1Neglecting minor losses in the pipes determine the
flows in the pipes
and the pressure heads at the nodes.
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Example 1
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7.2 Nodal method (Quantitybalance method) This method suites
branched network.
Figure 12 Flow in a branched network
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The basis of the method is as follow:1. Assume the head Hj at
each junction
2. Calculate the discharge flowing in each pipe, Qi
3. If at each junction we verify that Qi=0 then the solutionis
correct.
4. If Qi0, then apply a correction factor H to Hj and
return to (2), where
(36)fii
i
hQ
QH
/
2
