Agriculture Reference
In-Depth Information
1.3.2.1 Static and Dynamic Head
In reference to Fig. 1.8 the pressure of water at point “A” in the pipeline, when the
pipe is closed (water is static, not flowing), is
P
= ρ
h
It does not matter what the distance is of the point from the top of the source, that
is, static pressure is just for elevation difference. If we measure the pressure with the
water flowing, the pressure would be termed as “dynamic pressure.”
Fig. 1.8 Water tank showing
static pressure
h
A
1.3.2.2 Pressure Distribution in a Water Column/Tank
Consider a tank of water as shown in Fig. 1.9 . At the top surface of water, the
pressure is zero.
The pressure increases with the water depth. At the bottom of the tank (having
water depth of “ h ”), the intensity of pressure would be “
ρ
h.
Pressure Vs Flow Rate Relationship
There is an inverse relationship between pressure and flow. For a pipe of particu-
lar size, higher pressure means lower flow. Lower pressure results in higher flows.
This is because as the total energy is constant, higher pressure head results in lower
velocity head (and hence lower velocity), thus lower flow rate.
0
h
Fig. 1.9 Schematic of
pressure distribution in a
vertical water tank
ρh
 
 
 
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