Environmental Engineering Reference
In-Depth Information
7.2.2 Network Pressure Buffer
The length of pipes is indirectly included into the power balance in Equation 7.2 (and
consequently in Equation 7.4) through the amount of friction loss
h
f,j
that grows
proportionally to the pipe length. Analyses of the network pressure buffer expose more
significant impact of pipe lengths and nodal elevations i.e. the topography on the network
reliability.
Figure 7.1
Pipe pressure buffer
The dashed area shown in Figure 7.1 represents this buffer. For a pipe section 1 - 2 having
the length of
L
1-2
, the pressure buffer is calculated from the dashed polygon:
p
+
p
(
)
2
2
7.5
pb
=
1
2
L
−
z
−
z
1
−
2
1
−
2
1
2
2
ρ
g
Similarly, the area of the triangle defined by the friction loss is calculated as:
h
(
)
2
f
,
−
2
2
hl
=
L
−
z
−
z
7.6
1
−
2
1
−
2
1
2
2
An index that describes the ratio of the values from Equations 7.5 and 7.6 will eventually be
indirectly dependent on the pipe length hidden in the friction loss value, as is the case in
Equations 7.2 and 7.4. The
pressure buffer index
of pipe
j
,
PBI
j
, is calculated as:
h
f
,
j
PBI
=
1
−
ρ
g
7.7
j
p
+
p
1
j
2
,
j
and for the entire network:
1
m
∑
=
PBI
=
PBI
7.8
j
m
j
1
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