Calculating duct resistance, Planning drop downs – Grizzly G0601 User Manual
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Model g0442/g0601 (Mfg since 3/12)
figure 55. static pressure loss charts.
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"
0.091
0.122
0.35
0.453
2.5"
0.08
0.107
0.306
0.397
3"
0.071
0.094
0.271
0.352
4"
0.057
0.075
0.215
0.28
5"
0.046
0.059
0.172
0.225
6"
0.037
0.047
0.136
0.18
7"
0.029
0.036
0.106
0.141
8"
0.023
0.027
0.08
0.108
9"
0.017
0.019
0.057
0.079
fitting
dia.
90˚
elbow
45˚
elbow
45˚
Wye(y)
90˚
Wye(y)
3"
0.47
0.235
0.282
0.188
4"
0.45
0.225
0.375
0.225
5"
0.531
0.266
0.354
0.236
6"
0.564
0.282
0.329
0.235
7"
0.468
0.234
0.324
0.216
8"
0.405
0.203
0.297
0.189
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,
including the length, and multiply those num-
bers by the static pressure value given in the
previous table.
2. List each type of elbow or branch and multiply
the quantity (if more than one) by the static
pressure loss given in the previous table.
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 following tables to
calculate the resistance of duct work.
calculating duct resistance
To Planer
Blast Gate
Flex Pipe
Rigid Pipe
Rigid Pipe
(Main Line)
Elbow
Clamp
Y Branch
figure 54. drop down setup.
planning drop downs
plan all the drop downs for each machine with
blast gates, as shown in the
figure below.
plan the drop downs for each machine, using
blast gates wherever possible to control airflow.