Hydraulics & Hydrology
Review
Lecture3
Dr. Jawad Al-rifai
1
WATER PRESSURE
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Mass per unit volume is referred to as the density
of a fluid.
The density of water at temp. 15C & pressure of 1
atmosphere is 999kg/m3
The force exerted by gravity on 1.0 cu ft (1.0 m3)
of water is 62.4 lb (9.80 kN);
eq density X gravity (32.2ft/s2; 9.81m/s2 )
Pressure is the force exerted per unit area
Water pressure is exerted equally in all directions,
and increases linearly with depth
◦ Pressure in psi is equal to 0.433 times the depth in feet
◦ Pressure in KPa is equal to 9.8 times the depth in meter
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3
A piezometer consists of a
small tube rising from a
container of water under
pressure
The height of the water in
the tube denotes
the pressure of the
confined water
Water pressure is
commonly
measured by a Bourdon
gauge
A mercury column can be
used to measure relatively
high pressure values
4
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If the pressure measured is greater than
atmospheric, this value is sometimes called
gauge pressure
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If the pressure measured is less than
atmospheric,
it is referred to as a vacuum
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Absolute pressure is the term used for a
pressure reading that includes atmospheric
pressure
◦ The pressure relative to absolute zero
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4–2 PRESSURE-VELOCITY-HEAD
RELATIONSHIPS
The association between quantity of water
flow,
average velocity, and cross-sectional area
of flow is given by the equation
This formula is known as the continuity
equation
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For an incompressible fluid such as water:
If cross-sectional area decreases,
velocity of flow must increase
If the area increases, the velocity
decreases
8
Total energy in a hydraulics system is equal
to the sum of elevation head + pressure
head + velocity head
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11
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Valves, fittings, and other appurtenances
disturb
the flow of water, causing losses of head
◦ In addition to the friction loss in the pipe
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Distribution system losses due to
appurtenances are relatively insignificant
compared to pipe friction losses
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In pumping stations & treatment plants,
minor losses in valves & fittings are a
major part of the total losses
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4–2 PRESSURE-VELOCITY-HEAD RELATIONSHIPS
Unit head losses may be expressed as being
equivalent to the loss through a certain
length of pipe or by the formula
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