Set the flow, aperture and through-screen velocity — get the screen area, the clean and clogged
headloss (your clog-alarm threshold), and the channel or drum geometry. The step that protects membranes
and MBBR carriers downstream from rags and grit.
1Duty & screen
Fine screens (1–6 mm) follow coarse bar screens; drum screens rotate the mesh out of the channel. Size area by through-screen velocity (0.3–0.9 m/s).
Results — area & headloss
Screen area A
—m²
Clean Δh
—mm
Clogged Δh
—mm
Item
Value
Basis
2Geometry
Channel screen: height from area ÷ width. Drum screen: length from area ÷ (π·D·capture).
Item
Value
Basis
Screening envelope
Item
Value
Basis
Quote the screen instruments at factory price
A fine screen needs a level-differential transmitter across the mesh (clog alarm), a flowmeter, and
the rake/brush drive signal — mappable to our catalogue and supplied at the manufacturer's ex-works price
(margin from the export rebate only).
Headloss Δh = K·v²/(2g); clean K≈0.5, clogged K = clog factor (≈2.5 at ~50% blinding). The clogged value is the differential-alarm setpoint.
Full derivation and worked example: Fine-Drum-Screen-Calculation-Sheet.md. Fine screening protects the biology and any downstream membrane — run it, then carry Q into the grit chamber.
