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Sizing and Technical
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The Filter Stepper® Screen
Sizing and Technical Information
Flow vs. Channel Width vs. Headloss for 6 mm Filter Stepper Screen
Graph assumes: V1 = 2 fps and D = 2 (C) |
Recommendations for Designing a Channel
 Maintain V1 above 2 fps to ensure scouring
Keep V1 acceptable during off-peak flows by setting D = 2 (C)
Channel Depth = D + 12" freeboard
Narrower grid openings will reduce efficiency |
Conversion Factors
Headloss in inches = (V22-V12)(0.186) where V1 and V2 are in ft/s
Flow 1 mgd = 694.44 gal/min = 1.5472 ft3/s
Length 1 ft = 0.3048 meters
1 in = 2.54 centimeters
Volume 1 ft3 = 7.4805 gallons = 28.317 liters |
Example Calculation for Existing Channel
Given: C = 2' D = 4' V1 = 2 fps
G = C - 5" = 19"
Q = C (D) V1 = 36 ft3/s = 10.34 mgd
To determine headloss for a 6 mm grid with clean screen
find: Open Area = G (D-3") eff = 3.74 ft2
V2 = Q / Open Area = 4.27 fps
h = (V22-V12) 0.186
h= 2.65 in |
Nomenclature
C = channel width
D = depth of flow
G = grid width = D - 5"
Q = flow
h = headloss
V1 = Inlet Velocity
V2= Exit Velocity
eff = grid efficiency |
Channel Schematic
3" Hyd. Jump |
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Screen Opening Sizes |
2.5mm |
4mm |
6mm |
9mm |
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Open Area % with clean screen |
44.06 |
51.07 |
63.04 |
68.68 |
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Open Area % with 30% blocked |
30.84 |
35.75 |
44.13 |
48.08 |
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Note: |
Grid eff = Grid Open Area / Grid Total Area
Screen eff = Grid Open Area / Flow Area
Grid Open Area = Grid Total Area - Grid Closed Area (due to the static and dynamic grid elements)
Flow Area = (C) (D)
Grid Width (G) = Channel Width (C) - 5" |
