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PREFERRED
(Standard)
NOT ACCEPTABLE
POOR
Various Elbows Showing Radius Ratios
FIG. 2.3
R
RR =
W
Radius Ratio (RR)
or RR = 1.5
FIG. 2.4
R b
R a
CR =
W
Curve Ration (CR)
Optimum Reading CR = .05
FIG. 2.5
CR =
R1 = 2 Ra
R
1
CR = .25
R b
R a
CR =
R1 = 2 Ra
R
1
R2 =
R 2
R b
CR = .15
R a
FIG. 2.6
Using Splitters to reduce resistance.
INSTALLATION INSTRUCTIONS
FAIR
D
R
W
D
R a
R b
Ra
Rb
Ra
Rb
(Rb - R1)
2
+ Ra
E D D I E S
ITEM 1
Sharp Angle
E D D I E S
ITEM 2
Rounded
Outer
Corner
ITEM 3
Rounded
Corners
FIG. 2.7
Different ways of making a 90 degree bend. Some
involve greater pressure losses than others.
LARGE DUCT
FIG. 2.8
Pressure losses occur with abrupt reducing fittings.
ABRUPT EXPAN-
S I O N
SMALL
D U C T
E D D Y
LOSSES
FIG. 2.9
Abrupt expansion results in excessive pressure losses.
6
ITEM 4
Long Radius Bend
ITEM 5
Splitters, or turning vanes
installed in sharp angle
bend
ITEM 6
Splitters in rounded
corner bend
A B R U P T
CONTRACTION
SMALL
E D D Y
D U C T
LOSSES
LARGE
D U C T
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