Duct fitting pressure drop coefficients for
rectangular and round diverging wyes

From ASHRAE (1989), with permission

A5-6i.gif (11905 bytes)

Branch Cc,b for q = 45°

Vb / Vc

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Ab / Ac

0.8

0.78

0.62

0.49

0.40

0.34

0.31

0.32

0.35

0.40

0.7

0.77

0.59

0.47

0.38

0.34

0.32

0.35

0.41

0.50

0.6

0.74

0.56

0.44

0.37

0.35

0.36

0.43

0.54

0.68

0.5

0.71

0.52

0.41

0.38

0.40

0.45

0.59

0.78

1.0

0.4

0.66

0.47

0.40

0.43

0.54

0.69

0.95

1.3

1.7

0.3

0.66

0.48

0.52

0.73

1.2

1.8

2.7

3.7

4.9

0.2

0.56

0.56

1.0

1.8

3.2

4.9

7.1

9.6

13

0.1

0.60

2.1

5.1

9.3

16

-

-

-

-


Branch Cc,b for q = 90°

Vb / Vc

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Ab / Ac

0.8

0.95

0.92

0.92

0.93

0.94

0.95

1.1

1.2

1.4

0.7

0.95

0.94

0.95

0.98

1.0

1.1

1.2

1.4

1.6

0.6

0.96

0.97

1.0

1.1

1.1

1.2

1.4

1.7

2.0

0.5

0.97

1.0

1.1

1.2

1.4

1.5

1.8

2.1

2.5

0.4

0.99

1.1

1.3

1.5

1.7

2.0

2.4

3.0

3.6

0.3

1.1

1.4

1.8

2.3

3.2

4.3

5.5

6.9

8.5

0.2

1.3

1.9

2.9

4.1

6.2

8.5

11

-

-

0.1

2.1

4.8

8.9

14

-

-

-

-

-


Main Cc,s for q = 90°

vs / vc

0

0.1

0.2

0.3

0.4

0.5

0.6

0.8

1.0

Cc,s

0.40

0.32

0.26

0.20

0.14

0.10

0.06

0.02

0