EngiMetric Arena / Interpret & Validate
Can a filter submittal claim 0.45 m of calculated head loss?
Competency Evidence interpretation primary Constraints and trade-offs supporting
What you should take away: Recognise when a number is outside the engine's basis and require the missing media or test data instead of treating a plausible value as calculated.
The situation
What is happening
A filter sizing sheet lists 150 m3/h, a 10 m/h filtration rate, 1.2 m water depth, 0.8 mm media and 5 m2 unit area. The calculated area is 15 m2, the design area 16.5 m2 and the unit count 4. The submittal then states "clean-water head loss: 0.45 m, calculated". The engine reports that head loss is not computed because it depends on media depth, grain size, specific gravity, void fraction, flow and fouling. Choose the defensible interpretation.
Given
| Quantity | Value | Unit | Note |
|---|---|---|---|
| Design flow | 150 | m3/h | Filter influent flow. |
| Filtration rate | 10 | m3/m2/h | Engineer-selected rate. |
| Water depth | 1.2 | m | Above the media. |
| Media effective size | 0.8 | mm | Recorded, not used to derive head loss. |
| Unit area | 5 | m2 | Catalogue area per filter. |
| Claimed head loss | 0.45 | m | Stated as calculated in the submittal. |
Assumptions this challenge makes
- The sizing inputs are the values the engine accepts.
- The 0.45 m claim is presented as a calculated clean-water head loss.
- No media manufacturer curve or laboratory head-loss test is included in the submittal.
Your call
Your answer
Hints
- Look at what the engine actually returns. Does it include a head-loss number?
- The engine names the variables head loss depends on. Are any of them in the submittal?
- A number can be plausible and still be unsupported. What evidence would make it calculated?
Your answer Engine result
Where that comes from
Each limit, checked
Why
- The engine derives a required area of 150 / 10 = 15 m2, a design area of 16.5 m2 and 4 units at 5 m2 each.
- It reports media volume, but it does not report head loss. Its basis statement names media depth, grain size, specific gravity, void fraction, flow and fouling as the missing dependencies.
- The 0.45 m claim is therefore outside the engine's basis. It may be a real manufacturer value, but the submittal has not shown the curve or test that would establish it.
- The defensible action is to request the media head-loss curve or a laboratory test at the design flow, then check the clean and dirty-bed values.
- The area calculation remains valid. The challenge is about not letting a valid area result lend false authority to an unrelated head-loss claim.
What this challenge does not establish
- The engine is a sizing tool, not a media head-loss model.
- A manufacturer curve is itself a claim that must be checked for flow, temperature and media condition.
- The calculation does not assess backwash, bed expansion or air scour.
- The 0.45 m value is not proven wrong; it is shown to be unsupported by the stated basis.