Woodstock SHOP FOX W1687 - Manual (Page 27)

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Plan the drop downs for each machine, using blast gates
wherever possible to control airflow.
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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).
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(% 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.
)% 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.
*% Add the additional factors from the table below to
your list.
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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
=`^li\*/%Lower static pressure loss
chart.
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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
=`^li\*.%Upper static pressure loss
chart.
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Seasoned Dust Collection Filter 5"
Entry Loss at Large Machine Hood 2"
=`^li\*,%Additional factors affecting static pressure.