# Pipe Networks - NRCS Irrigation ToolBox ```Pipe Networks
Pipeline
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systems
pipe
networks
measurements
manifolds and diffusers
Pumps
Monroe L. Weber-Shirk
School of Civil and
Environmental Engineering
Pipeline systems:
Pipe networks
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

Water distribution systems for municipalities
Multiple sources and multiple sinks connected
with an interconnected network of pipes.
Computer solutions!




KYpipes
CyberNET
EPANET http://www.epa.gov/ORD/NRMRL/wswrd/epanet.html
Water Distribution System
Assumption
Each point in the
system can only
have one _______
pressure
The pressure change
from 1 to 2 by path a
must equal the
pressure change
from 1 to 2 by path b


a
1
2
b
V12
p2 V22

 z1  
 z 2  hL
 2g
 2g
p1
p2


p1


V12
a
2g
 z1 
V22
a
2g
 z 2  hL
a
Water Distribution System
Assumption
V12
a
2g
 z1 
V22
a
2g
 z 2  hL 
a
V12
b
2g
Pressure change by path a
hL  hL
a
b
 z1 
V22
b
2g
 z 2  hL
b
a
1
b
zero
Or sum of head loss around loop is _____.
(Need a sign convention)
Pipe diameters are constant
 Model withdrawals as occurring at nodes so
V is constant

2
Pipes in Parallel

Find discharge given pressure at A and B
 ______&amp;
energy

flows
____
S-J equation
Qtotal A
Q1
Q2
B
Find head loss given the total flow
a discharge Q1’ through pipe 1
 solve for head loss using the assumed discharge
 using the calculated head loss to find Q2’
 assume that the actual flow is divided in the same
_________
proportion as the assumed flow
 assume
Networks of Pipes
conservation at
 Mass
____ __________
all nodes
loss and discharge must be
maintained for each pipe
 Darcy-Weisbach

A
0.28 m3/s
?
equation
_____________
Swamee-Jain
 Exponential

0.32
m3/s
a
friction formula
_____________
Hazen-Williams
1
2
b
Network Analysis
Find the flows in the loop given the inflows
and outflows.
The pipes are all 25 cm cast iron (e=0.26 mm).
0.32 m3/s
A
B
C
D
0.28 m3/s
100 m
0.10 m3/s
200 m
0.14 m3/s
Network Analysis
Assign a flow to each pipe link
 Flow into each junction must equal flow out
of the junction

arbitrary
0.32 m3/s
0.32
0.00
0.10 m3/s
0.28 m3/s
B
A
0.04
C
D
0.10
0.14 m3/s
Network Analysis

Calculate the head loss in each pipe
 8 fL  2
h f   5 2 Q
gD  
f=0.02 for Re&gt;200000
A
1
B
h f  0.222m
2
h f  3.39m
C
h f  0.00m
4
4
h
fi
 31.53m
i1
0.28 m3/s
2
4
0.10 m3/s
1
3
h f = kQ Q Sign convention +CW
k1,k3=339
 8(0.02)(200) 
  339
k1  
k2,k4=169
 (9.8)(0.25)5  2 


0.32 m3/s
h f  34.7m
3
D
0.14 m3/s
Network Analysis


The head loss around the loop isn’t zero
Need to change the flow around the loop



clockwise flow is too great (head loss is
the ___________
positive)
reduce the clockwise flow to reduce the head loss
Solution techniques



Hardy Cross loop-balancing (___________
_________)
optimizes correction
Use a numeric solver (Solver in Excel) to find a change
in flow that will give zero head loss around the loop
Use Network Analysis software
Numeric Solver





Set up a spreadsheet as shown below.
the numbers in bold were entered, the other cells are
calculations
initially Q is 0
use “solver” to set the sum of the head loss to 0 by changing Q
the column Q0+ Q contains the correct flows
∆Q
pipe
P1
P2
P3
P4
0.000
f
0.02
0.02
0.02
0.02
L
200
100
200
100
D
0.25
0.25
0.25
0.25
k
Q0 Q0+∆Q
339 0.32 0.320
169 0.04 0.040
339 -0.1 -0.100
169
0 0.000
hf
34.69
0.27
-3.39
0.00
31.575
Solution to Loop Problem
Q0+ Q
0.218
0.062
0.202
0.102
0.32 m3/s
1
A
0.218
4
2
0.102
0.10
m3/s
C
0.28 m3/s
B
0.062
0.202
3
D
0.14 m3/s
Better solution is software with a GUI showing the pipe network.
Pressure Network Analysis
reservoir
pipe
0.32 m3/s
junction
1
A
0.218
4
2
0.102
0.10
m3/s
C
0.28 m3/s
B
0.062
0.202
3
D
0.14 m3/s
Network Elements

Controls








Check valve (CV)
Pressure relief valve
Pressure reducing valve (PRV)
Pressure sustaining valve (PSV)
Flow control valve (FCV)
Pumps: need a relationship between flow and head
Reservoirs: infinite source, elevation is not
affected by demand
Tanks: specific geometry, mass conservation
applies
Check Valve
Valve only allows flow in one direction
 The valve automatically closes when flow
begins to reverse

open
closed
Pressure Relief Valve
pipeline
closed
open
relief flow
Low pipeline pressure
High pipeline pressure
Valve will begin to open when pressure in
exceeds a set pressure
the pipeline ________
(determined by force on the spring).
Pressure Regulating Valve
sets maximum pressure downstream
closed
High downstream pressure
open
Low downstream pressure
Valve will begin to open when the pressure
less
downstream
___________ is _________
than the setpoint
pressure (determined by the force of the spring).
Pressure Sustaining Valve
sets minimum pressure upstream
closed
Low upstream pressure
open
High upstream pressure
Valve will begin to open when the pressure
upstream is _________
greater than the setpoint pressure
________
(determined by the force of the spring).
Similar to pressure relief valve
Flow control valve (FCV)
Limits the ____
___
flow rate
through the valve to a
specified value, in a
specified direction
 Commonly used to limit
the maximum flow to a
value that will not
provider’s system

Pressure Break Tanks




In the developing world small water supplies in
mountainous regions can develop too much
pressure for the PVC pipe.
They don’t want to use PRVs because they are too
expensive and are prone to failure.
Pressure break tanks have an inlet, an outlet, and
an overflow.
Is there a better solution?
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