Environmental Engineering Reference
In-Depth Information
2.5.4 Total dynamic head (Total system head)
Total Head = Static Head + Friction Head + Velocity Head
(2.9)
2.5.5 Calculating head if Pressure is Known
The pressure exerted by water/wastewater is directly proportional
to its depth or head in the pipe, tank, or channel. If the pressure is
known, the equivalent head can be calculated:
Head (ft) = Pressure (psi) × 2.31 ft/psi
(2.10)
Example 2.8
Problem:
The pressure gauge on the discharge line from the influent
pump reads 72.3 psi. What is the equivalent head in feet?
Solution:
Head = 72.3 × 2.31 ft/psi = 167 ft
2.5.6 Calculating Pressure if head is Known
If the head is known, the equivalent pressure can be calculated by:
Head (ft)
2.31 ft/psi
Pressure (psi)
=
(2.11)
Example 2.9
Problem:
The tank is 22 ft deep. What is the pressure in psi at the bot-
tom of the tank when it is filled with water?
Solution:
22 ft
2.31 ft/psi
Pressure (psi)
=
=
9.52 psi(r
ounded)
2.6 floW/disCharge raTe: WaTer in MoTion
The study of fluid flow is much more complicated than that of flu-
ids at rest, but it is important to have an understanding of these prin-
ciples because the water in a waterworks and distribution system and
in a wastewater treatment plant and collection system is nearly always
in motion.
discharge
(or flow) is the quantity of water passing a given
point in a pipe or channel during a given period. Stated another way
for open channels: The flow rate through an open channel is directly
