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15 2 Calculating the discharge rate from the water-jet
The following table and calculation is used to determine
the discharge rate of a pump system with a given pipe
diameter by measuring the water-jet with a simple tool
(angle bracket).
CAUTION – Keep in mind that this
method is just an approximation
and does not replace professional
flow sensors
15 1 5 How to measure the discharge rate
1.
Start the pump system.
2.
Wait until the pump gives continuous discharge.
3.
Use an angle bracket, best with a scale on both legs.
4.
Put the angle bracket straight onto the pipe like
shown in "Figure 33: Reading off the discharge rate
according to the pipe diameter"below.
5.
Read off the discharge rate according to the pipe
diameter
6.
Note the value "a". Make sure b, i.e. the other leg, is
adjusted to 4'' at the water-jet surface.
NOTE – The pipe´s wall thickness is
ignored The measure result
depends on the measuring
precision
15 1 6 How to calculate the discharge rate
The following examples show how the discharge rate has
been calculated for table X
Formulas needed:
Q = v . A
Constraints:
Q
= Flow rate
v
= velocity field
A
= pipe cross-sectional vector area
a
= value for discharge length of water-jet
b
= value for drawdown of water-jet
g
= earth's gravity, by definition,
9.81 m/s² / 32.17 ft/s²
d
= pipe diameter
BERNT LORENTZ GmbH & Co. KG Kroegerskoppel 7, 24558 Henstedt-Ulzburg, Germany, Tel. +49 (0) 4193 7548 - 0, Fax - 29, www.lorentz.de
All specifi cations and information are given with good intent, errors are possible and products may be subject to change without notice. Pictures may
differ from actual products depending on local market requirements and regulations.
15 1 7 Calculation example 1
This example is done in the US system.
a: 15"
b: 5"
d: 2"
Calculation:
Using formula B.2:
Using formula B.3:
/s ≈ 0.2598 GPM (US) as well as v
With conversion 1 in
3
and A inserted into formula B.1 follows:
With the given values the approximated discharge rate of
the pump system is about 76 GPM.
B.1
B.2
Figure 33: Reading off the discharge rate according to the pipe diameter
B.3
d
34
15 1 8 Calculation example 2
This example is done in the metric system.
a: 30 cm = 0.3 m
b: 15 cm = 0.15 m
d: 3" = 7.62 cm = 0.0762 m (1" = 2.54 cm)
Calculation:
Using formula B.2:
Using formula B.3:
With v and A inserted into formula B.1 follows:
With the given values the approximated discharge rate of
the pump system is about 28 m
3
/h.
a
Sun. Water.
b
Life.
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