Duct fitting pressure drop coefficients for
round elbows with three, four, and five pieces

From ASHRAE (1989), with permission

The pressure drop coefficient is given by C = Kq · C90

A5-6c.gif (14253 bytes)

Coefficients for 90° elbows (C90)

Number of pieces

r/D

0.75

1.0

1.5

2.0

5

0.46

0.33

0.24

0.19

4

0.50

0.37

0.27

0.24

3

0.54

0.42

0.34

0.33

Angle correction factors Kq

q

0

20

30

45

60

75

90

110

130

150

180

Kq

0

0.31

0.45

0.60

0.78

0.90

1.00

1.13

1.20

1.28

1.40