-22-
g1028z/g1029z dust Collector
Calculating Duct Resistance
adding duct work, elbows, branches and any
other components to a duct line increases airflow
resistance (static pressure loss). this resistance
can be minimized by using rigid (smooth) pipe and
gradual curves, as opposed to flexible pipe and
90˚ elbows.
to help you think about this resistance, imagine
riding a bicycle in a tunnel that is an exact replica
of your duct work. if the inside of the tunnel is very
bumpy (flexible pipe) and has a lot of sharp turns
(90˚ elbows), it will take a lot more effort to travel
from one end to the other.
the purpose of calculating the resistance is to
determine if it is low enough from the machine to
the dust collector to meet the given CFm require-
ment for the machine. use the charts in
figure 25
to calculate the resistance of duct work.
Duct
Dia.
approximate
Static pressure
Loss per foot of
Rigid pipe
approximate
Static pressure
Loss per foot
of flex pipe
main
lines
at 3500
Fpm
Branch
lines
at 4000
Fpm
main
lines
at 3500
Fpm
Branch
lines
at 4000
Fpm
2"
.091
.122
.35
.453
2.5"
.08
.107
.306
.397
3"
.071
.094
.271
.352
4"
.057
.075
.215
.28
5"
.046
.059
.172
.225
6"
.037
.047
.136
.18
7"
.029
.036
.106
.141
8"
.023
.027
.08
.108
9"
.017
.019
.057
.079
fitting
Dia.
90˚
Elbow
45˚
Elbow
45˚
Wye(y)
90˚
Wye(y)
3"
.47
.235
.282
.188
4"
.45
.225
.375
.225
5"
.531
.266
.354
.236
6"
.564
.282
.329
.235
7"
.468
.234
.324
.216
8"
.405
.203
.297
.189
figure 25. static pressure loss charts.
additional factors
Static pressure
seasoned (well used)
dust Collection Filter
1"
entry loss at large
machine hood
2"
in most small/medium shops it is only necessary
to calculate the line with the longest duct length or
the most fittings (operating under the assumption
that if the line with the highest resistance works,
the others will be fine).
To calculate the static pressure of any given
line in the system, follow these steps:
1. make a list of each size duct in the line, includ-
ing the length, and multiply those numbers by
the static pressure value given in
figure 25.
2. list each type of elbow or branch and multiply
the quantity (if more than one) by the static
pressure loss given in
figure 25.
3. add the additional factors from figure 26 to
your list.
figure 26. additional factors affecting static
pressure.
4. total your list as shown in the example in
figure 27 to come up with your overall static
pressure loss number for that line.
Note:
Always account for a seasoned filter,
so you don't end up with a system that only
works right when the filter is clean.
figure 27. totaling static pressure numbers.
Main Line
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Elbows/Branches
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Additional Factors
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Total Static Pressure Loss ................ 4.444
