Media filter sizing
Convert vessel diameter (inches or mm) to bed area and calculate service and backwash flow from design linear velocities for sand, glass (AFM), catalytic and carbon media beds.
= 254 mm. Vessel designations quote inches: a 1054 vessel is 10" diameter, a 2472 is 24".
The two velocities are typical design values for the selected filter media, and re-fill whenever you change the media above. They are assumptions, not measurements — overwrite either one to match your media supplier’s datasheet and the results recalculate immediately. Clack quotes 37–49 m/h backwash for fine (0.45–0.55 mm) sand with 20% freeboard minimum, which matches conventional rapid-sand practice; the default here is the bottom of that band. Coarser and denser gradings need MORE upflow to fluidise, not less, and cold water needs less than warm for the same expansion — so confirm the rate against your actual grading and the coldest water the filter will see, then check the valve and the drain can pass it. DWT standard fills allow ~30% freeboard.
Results
| Bed area | 0,051 m2 |
|---|---|
| Service flow | 0,91 m3/h (15 L/min) |
| Backwash flow required | 1,87 m3/h (31 L/min) |
| Fill and freeboard | Settled bed ~77% of vessel volume; freeboard ≥30% of bed depth (bed expands ~20% in backwash) |
Size on linear velocity, not vessel volume — and check the whole train can deliver the backwash flow: an undersized valve or feed pump is the usual cause of a failed media filter, especially with catalytic iron-removal media. Fill to the media’s design fraction and keep the freeboard above the settled bed — an over-filled vessel backwashes its media to drain. Support fine media on graded gravel unless the vessel has a false-bottom distributor.
Formula used
A = π × d² ÷ 4
Qs = A × vs
Qb = A × vb
- A
- bed cross-sectional area, m2
- d
- vessel internal diameter, m
- Qs
- service flow, m3/h
- Qb
- backwash flow, m3/h
- vs
- service linear velocity, m/h
- vb
- backwash linear velocity, m/h
Media filters are sized on linear velocity through the bed cross-section, not on vessel volume. Preset velocities, expansion and freeboard figures are per-media design values from the manufacturers' data sheets (Clack, Dryden Aqua, Rotocarb ProCarb-900, Calgon, Jacobi, Purolite, and DWT's calcite sheet) — editable above; confirm against the specific media's datasheet, and check bed depth separately for contact-time-critical duties such as activated carbon.
Equipment for this duty
Send the water analysis and duty point, and the branch confirms exact selections, pricing and lead times — usually within one working day.
Request a quoteResults are indicative engineering estimates based on standard formulas and typical assumptions. They are not a design service; confirm any design against a full water analysis and the relevant manufacturer’s data.