Environmental Engineering Reference
In-Depth Information
3.2.5 velocity head
velocity head
is the amount of head or energy required to maintain
a stated velocity in the suction and discharge lines. The design of most
pumps makes the total velocity head for the pumping system zero.
Note:
Velocity head only changes from one point to another on a pipe-
line if the diameter of the pipe changes.
Velocity head and total velocity head are determined by:
Velocity
2
2
Velocity Head (ft)
=
(3.11)
g
TotalVelocityHead (ft)VelocityHead Disc
=
harge (ft)
Velocity Head Suction (ft)
(3.12)
−
Example 3.7
Problem:
What is the velocity head in a system with a velocity of 5 fps?
Solution:
2
Velocity
2
Velocity Head
=
g
2
22
(5 fps)
232ft/s
25 ft /s
64 ft/s
=
=
=
0.39 ft
2
2
×
Note:
A static system has no velocity head, as the water is not moving.
3.2.6 Total head
Total head
is the sum of the static, friction, and velocity heads:
TotalHead (ft)StaticHead (ft)FrictionH
=
+
ead (ft)
(3.13)
+
Velocity Head (ft)
3.2.7 Conversion of Pressure head
Pressure is directly related to the head. If liquid in a container sub-
jected to a given pressure is released into a vertical tube, the water will
rise 2.31 ft for every pound per square inch of pressure. To convert pres-
sure to head in feet:
Head (ft) = Pressure (psi) × 2.31 ft/psi
(3.14)