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 media, not measurements: overwrite either to match your supplier’s datasheet.
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.
Notes on this media
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.
Parts for a 10" x 54" filter
Typical catalogue parts for the 10" x 54" FlowShell vessel at this diameter; the valve shown is the smallest rated for the larger of the service and backwash flows. The branch confirms the final kit with your quote.
Pressure vessel
FRP1054Fibreglass pressure vessel 10" x 54", 2.5" top opening (62.5 L)
Ex-stock (0–3 days)Ex-stock
Control valve
F67C1Runxin F67C1 automatic backwash filter valve, 2.5" tank thread, 4 m³/h
Ex-stock (0–3 days)Ex-stock
Riser pipe
RISER1.4Riser pipe 27 mm, 1.4 m, for 844, 1054 and 1354 vessels
Ex-stock (0–3 days)Ex-stock
Bottom distributor
DISTBOT27Bottom distributor for 27 mm riser
Ex-stock (0–3 days)Ex-stock
Top distributor
DISTTOP27Top distributor for 27 mm riser
Ex-stock (0–3 days)Ex-stock
- This media is not in the online catalogue yet: ask the branch to quote it with the vessel.
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.
The background
- How a media filter actually works: linear velocity, bed depth and freeboardA media filter is a bed of particles doing depth filtration, and three design numbers decide whether it works or merely looks like it does.
- Backwashing: why, when, and what goes wrongBackwash is the half of media filtration that happens in reverse, and most long-term media filter failures turn out to be backwash failures.
- Filter media compared: sand, glass (generic vs AFM) and anthraciteSand is the benchmark and glass media promise more, though "glass" covers two very different products. Anthracite does its best work layered over sand. What each grain does in the bed.
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.