Labconco Coated Steel, Fiberglass and PVC Blowers 7183200 - Manual (Page 40)

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Chapter 7: Modifying Your Blower
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ductwork length for your entire hood/blower system. Then the
blower can be sized properly from the total equivalent resistance
for your exhaust system. Blower Sizing Example: You have
selected a Labconco Protector Premier 48 Laboratory Hood at 100
fpm and 730 CFM. The static pressure of the Protector Premier 48
at 100 fpm is 0.17". The exhaust collar of this hood is sized to
receive 12" diameter PVC duct directly. In this example, your
fume removal system requires 30 feet of straight duct, two 90°
elbows and one zero pressure weathercap to adequately exhaust the
chemical fumes. You will be handling low to moderately
corrosive materials, so you have selected a Coated Steel Blower.
The information following for the 90° elbow tells you that each
90°, 12" diameter elbow has the equivalent resistance of 25 feet of
straight duct. The zero pressure weathercap has 5 feet of
equivalent resistance. The total equivalent feet for the system is:
Feet of straight duct 30 Feet
2 elbows @ 25 feet each 50 Feet
1 zero pressure weathercap @ 5 feet 5 Feet
85 Feet
The chart following converts “equivalent resistance in feet of
straight duct” to static pressure. So the static pressure of 85
equivalent feet of 12" nominal duct is equal to (85/10) x 0.011" =
0.094". Now this is added to the hood static pressure of 0.17" for a
total system static pressure of 0.264". Look at the performance
data in Chapter 4 for Coated Steel Blowers. Refer to the 0.25"
column at 730 CFM since this is closest to 0.264". The chart will
lead you to select a Coated Steel Blower model #7068800 or EP
Coated Steel Blower #7068900.
Sizes and Pressure Losses in Thermoplastic Duct
This chart provides static pressure losses for 10' long duct lengths
of various diameters over a range of airflows in CFM for use in
sizing hood/blower combinations at 100 feet per minute.