Download - Water Management
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Water Management
Water is an important natural resource that requires proper management.
Appropriate flow rate, pressure, and water quality are necessary for effective use.
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Water System
WATER SUPPLY
STORAGE
TREATMENT
CONSUMER
DISTRIBUTION
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Supply
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Treatment
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Storage
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Consumer
1 psi = 2.31 ft of water
35-50 psi
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Terminology
Static pressure (head):No water flowing through the system
Head loss:Pressure loss due to friction
Actual pressure:Static pressure – head loss (all expressed in
psi)
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Hazen-Williams Formula
hf = 10.44 * L * Q1.85
C1.85 * d4.8655
Where: hf = head loss due to friction (ft) L = length of pipe (ft) Q = flow rate of water through
the pipe (gpm) C = Hazen-Williams constant d = diameter of the pipe (in.)
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Water Supply ProblemA business’s water supply connection at the street is at elevation 1,257 ft and has a pressure of 55 psi. The first floor fixture elevation is 1,285 ft. Between the connection and a first floor fixture, there are 120 ft of 3 in. copper pipe, 25 ft of ¾ in. copper pipe, and five (5) ¾ in. - 90o elbows. Discharge through the fixture is 10 gpm. The equivalent length for a single ¾ in., 90o elbow is 4 ft. The Hazen-Williams constant for copper pipe is 140.
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Water Supply Problem
What is the pressure loss due to elevation change between the street connection and the first floor fixture?
1st floor elevation – street elevation
1,285 ft – 1,257 ft = 28 ft
Convert to psi:
28 ft ÷ 2.31 ft/psi = 12.12 psi
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Total Equivalent Length of ¾ in. Pipe
= Pipe length + fitting equivalent length
= 25 ft + (5 elbows * 4 ft/elbow)
= 45.00 ft
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Head Loss in ¾ in. Pipe
Friction head loss using Hazen Williams equation
hf = 10.44 * L * Q1.85
C1.85 * d4.8655
hf = 10.44 * 45 ft * (10 gpm)1.85
(140)1.85 * (3/4 in.)4.8655
hf = 14.44 ft
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Head Loss in 3 in. Pipe
hf = 10.44 * L * Q1.85
C1.85 * d4.8655
hf = 10.44 * 120 ft * (10 gpm) 1.85
(140)1.85 * (3 in.) 4.8655
hf = 0.05 ft
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Total Head Loss for ¾ in. & 3 in. Pipe
Total Head Loss (due to friction):
= Head loss, ¾ in. pipe + head loss, 3 in. pipe
= 14.44 ft + 0.05 ft
= 14.49 ft
Convert to psi:
14.49 ft ÷ 2.31 ft/psi = 6.27 psi
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Water Supply Problem
What is the pressure in units of psi at the first floor fixture?
Actual pressure = street pressure – static difference – head loss
= 55 psi – 12.12 psi – 6.27 psi = 36.61 psi