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Model W1687 (For Machines Mfg. Since 9/11)
Planning.Drop.Downs
Plan the drop downs for each machine, using blast gates
wherever possible to control airflow.
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 requirement for the machine. Use
the provided tables to calculate the resistance of duct
work.
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,.do.these.steps:
1. Make a list of each size duct in the line, including
the length, and multiply those numbers by the static
pressure value given in the upper chart.
2. List each type of elbow or branch and multiply the
quantity (if more than one) by the static pressure
loss given in the lower chart.
3. Add the additional factors from the table below to
your list.
Additional.Factors
Seasoned Dust Collection Filter
Entry Loss at Large Machine Hood
Figure.35..Additional factors affecting static pressure.
Static.Pressure
5"
2"
-25-
Rigid Pipe
(Main Line)
Y Branch
Clamp
Flex Pipe
To Planer
Figure.36. Drop down setup.
Duct.
Approximate.
Dia.
Static.Pressure.
Loss.Per.Foot.of.
Rigid.Pipe
Main
Branch
Lines
Lines
at 3500
at
FPM
4000
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
Figure.37..Upper static pressure loss
chart.
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.38..Lower static pressure loss
chart.
Elbow
Rigid Pipe
Blast Gate
Approximate.
Static.Pressure.
Loss.Per.Foot.
of.Flex.Pipe
Main
Branch
Lines
Lines
at
at
3500
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
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