Calculating Duct Resistance - Grizzly G5954 Owner's Manual

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.
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 22
to calculate the resistance of duct work.
Duct Approximate
Dia. Static Pressure
Loss Per Foot of
Rigid Pipe
Main Branch
Lines Lines
at 3500 at 4000
FPM FPM
2" .091 .122
2.5" .08 .107
3" .071 .094
4" .057 .075
5" .046 .059
6" .037 .047
7" .029 .036
8" .023 .027
9" .017 .019
Fitting 90˚ 45˚
Dia. Elbow Elbow
3" .47 .235
4" .45 .225
5" .531 .266
6" .564 .282
7" .468 .234
8" .405 .203
Figure 22. Static pressure loss charts.
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).
G5954 5HP Dust Collector
Approximate
Static Pressure
Loss Per Foot
of Flex Pipe
Main Branch
Lines Lines
at 3500 at 4000
FPM FPM
.35 .453
.306 .397
.271 .352
.215 .28
.172 .225
.136 .18
.106 .141
.08 .108
.057 .079
45˚ 90˚
Wye(Y) Wye(Y)
.282 .188
.375 .225
.354 .236
.329 .235
.324 .216
.297 .189
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 22.
2.
List each type of elbow or branch and multiply
the quantity (if more than one) by the static
pressure loss given in Figure 22.
3. Add any additional factors from Figure 23.
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.
Additional Factors
Seasoned (well used)
Dust Collection Filter
Entry Loss at Large
Machine Hood
Figure 23. Additional static pressure factors.
4. Total your list as shown in Figure 24 to come
up with your overall static pressure loss.
Note: When determining static pressure loss
over multiple lines, only count the main line
numbers once.
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Figure 24. Totaling static pressure numbers.
5.
Compare the total static pressure loss for
that line to the closest CFM given in the
Performance Curve section on the data
sheet for your machine (located toward the
front of this manual).
Static Pressure
1"
2"
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