Page 219 - Water Engineering Hydraulics, Distribution and Treatment

EXAMPLE 6.6 DETERMINATION OF EQUIVALENT PIPE
Find the length of a 24 in. (600 mm) pipe with C = 100 that is equivalent to a 12 in. (300 mm) pipe with C = 130 and L = 2,000 ft
(610 m).
Solution:
At C = 130 read the C-factor 6.2 × 10 .
At d ∕d = 2.0, read the d-factor 2.9 × 10.
e
−1
Hence L ∕L = (6.2 × 10 )(2.9 × 10) = 18.
e
L = 2,000 × 18 = 36,000 ft (10,973 m)
e
6.6.4 Computer Programming −1 . 6.8 Management, Operation, and Maintenance of Distribution Systems 197
Of course at present, several handy commercial software
programs are available for modeling and design of water
High-speed computers can be programmed to solve network
systems (see Chapter 7). Software is available as a stand-
problems in a number of different ways. Convergence formu-
alone interface for Windows or integrated into GIS or CAD
las need not be introduced as such. Instead, the computer can
systems, for example:
be assigned the task of adjusting the water table or pressure
at each junction not controlled by a service reservoir until 1. Haestad Methods Solutions (Bentley Systems Inc.):
the circuit laws discussed in connection with the method of WaterGEMS and WaterCAD
relaxation are satisfied throughout the system. These laws
2. MWH Soft: InfoWater
can be summarized as follows:
3. Wallingford Software: InfoWorks WS (for water
1. At each junction ΣQ =ΣQ supply)
inflow outflow
2. In each circuit ΣH = 0
n
3. In each pipe H = kQ or Q = (H∕k) 1∕n 6.7 INDUSTRIAL WATER SYSTEMS
Toprogramtheoperation, number eachpipeandjunction Large industrial establishments, with a heavy investment in
and identify pipe ends by junction numbers. Then tabulate plant, equipment, raw materials, and finished products, con-
pipe resistances, junction pressures (including assumed centrated in a small area, are generally equipped with high-
values where pressures are unknown), and net inflows at each pressure fire supplies and distribution networks of their own.
junction (zero at all but entrance and exit points of the sys- Because such supplies may be drawn from sources of ques-
tem), and feed the tabulated information into the computer. tionable quality, some regulatory agencies require rigid sep-
The computer instructions are then as follows: calculate by aration of all private fire supplies and public distribution sys-
circuit law 3 the total flow into the first junction for which the tems. Others permit the use of protected cross-connections
water table elevation is unknown; adjust the assumed value and require their regular inspection for tightness. How the
until the total inflow and outflow are balanced in accordance two sources of supply can be divorced without denying the
with circuit law 1; proceed in sequence to the remaining protective benefit and general convenience of a dual supply
junctions; and readjust the first water table elevation. Repeat to industry is illustrated in Fig. 6.16. Ground-level storage
the cycle of operations until all circuit laws are satisfied. and pumping are less advantageous.
Camp and Hazen (1934) built the first electric analyzer A widely approved arrangement of double check valves
designed specifically for the hydraulic analysis of water dis- in vaults accessible for inspection and test by the provision
tribution systems. Electric analyzers use nonlinear resistors, of valves, gauges, and bleeders is shown in Fig. 6.17. No
called fluistors in the McIlroy analyzer, to simulate pipe outbreak of waterborne disease has been traced to approved
resistances. For each branch of the system, the pipe equa- and properly supervised cross-connections of this kind. Auto-
tion, H = kQ 1.85 , for example, is replaced by an electrical matic chlorination of the auxiliary supply can introduce a
equation, V = K I 1.85 , where V is the voltage drop in the further safeguard.
e
branch, I is the current, and K is the nonlinear-resistor coef-
e
ficient suited to pipe coefficient k for the selected voltage
6.8 MANAGEMENT, OPERATION, AND
drop (head loss) and amperage (water flow) scale ratios. If
MAINTENANCE OF DISTRIBUTION
the current inputs and takeoffs are made proportional to the
SYSTEMS
water flowing into and out of the system, the head losses will
be proportional to the measured voltage drops. Some large, For intelligent management of distribution storage, reser-
rapidly developing communities have found it economical to voir levels must be known at all times of the day and night.
acquire electric analyzers suited to their own systems. Where levels cannot be observed directly by gauges or floats,