Calculator Inputs
Formula Used
Step 1: Face velocity
Convert flow to m³/s and compute v = Q / A.
Using net open area improves accuracy for screens and discs.
Empirical option
ΔP = K · v². Here, K is multiplied by the fouling factor,
then adjusted lightly by filter type.
Porous media option
ΔP = (μ·L/k)·v + (ρ·β·L)·v².
The first term is viscous loss; the second grows faster at higher velocity.
How to Use This Calculator
- Enter flow and select your preferred unit.
- Use effective open area from the filter spec sheet.
- Choose a method based on the filter design.
- Increase fouling factor to represent clogging.
- Submit; results appear above the form.
Example Data Table
| Scenario | Flow (m³/h) | Area (m²) | Method | Fouling | Estimated ΔP (kPa) | Head (m) |
|---|---|---|---|---|---|---|
| Clean screen filter | 3.0 | 0.025 | Empirical | 1.0 | ~3–6 | ~0.3–0.6 |
| Partly clogged disc filter | 3.0 | 0.025 | Empirical | 3.0 | ~10–20 | ~1.0–2.0 |
| Media bed, moderate packing | 6.0 | 0.040 | Porous | 1.5 | Varies | Varies |
Examples are illustrative. Calibrate using your own gauge readings for best accuracy.
Operational context for irrigation filters
Pressure drop is the simplest field signal of filter condition. In drip and micro-sprinkler zones, stable outlet pressure supports uniform discharge and reduces emitter plugging. A clean filter often shows low losses at design flow, while a rising differential pressure indicates loading from algae, sand, rust, or organic fines. Tracking changes over time helps schedule flushing or backwash before the system falls below target pressure at the farthest emitters.
What the calculator measures
The calculator converts your flow to m³/s, then computes face velocity using effective open area. Results are reported in kPa, bar, psi, and head meters to match common irrigation gauges and design notes. Outlet pressure is estimated by subtracting the calculated loss from inlet pressure, providing a check of available pressure for downstream regulation and lateral sizing.
Empirical modeling for screens and discs
Many compact irrigation filters behave like a velocity-squared device, especially at higher flow rates. The empirical option uses ΔP = K·v², where K represents the combined effect of mesh size, disc stack geometry, turbulence, and minor losses. The fouling factor scales K so you can represent cleanliness states with one control: 1.0 for clean, 2–5 for partially loaded, and higher when flow paths narrow.
Porous media behavior in sand or gravel beds
Media beds can be modeled with Darcy–Forchheimer: ΔP = (μ·L/k)·v + (ρ·β·L)·v². The viscous term dominates at low velocity and tighter packing, while the inertial term grows rapidly as flow increases. Use this option when you know bed thickness and want to test how permeability changes with media selection, compaction, or backwash performance.
Using results for maintenance and design
Compare calculated drops against your field limits for differential pressure. If the model predicts a large loss at design flow, increase filter size, add parallel filters, or reduce velocity by increasing effective area. For maintenance, record inlet and outlet pressure; when the measured differential exceeds the baseline, increase flushing frequency or inspect upstream screening to reduce solids loading.
FAQs
1) What is “effective open area” and why does it matter?
It is the net flow area through the filter element, not the pipe area. Smaller open area increases face velocity, which increases pressure drop and can reduce downstream pressure.
2) When should I use the porous media option?
Use it for sand or gravel media beds, or any element that behaves like a packed porous layer. It accounts for viscosity and inertial effects, which can dominate in deeper beds.
3) How do I choose an empirical K value?
Start with a clean, measured pressure drop at a known flow. Rearranging gives K ≈ ΔP / v². Keep the same area and units, then adjust fouling to match dirty conditions.
4) What fouling factor should I enter for a dirty filter?
If your differential pressure is roughly triple the clean baseline at the same flow, use a fouling factor near 3. Use your gauge history to map fouling values to site conditions.
5) Why does filter type change the result slightly?
Different designs create different turbulence and internal loss paths. The type adjustment is a light multiplier to reflect typical behavior, not a substitute for calibrating to your equipment.
6) Can I use this for fertilizers or reclaimed water?
Yes, but update fluid density and viscosity if they differ from water. For reclaimed water with more solids, expect faster fouling and verify with real differential pressure readings.