Calculator Inputs
Use SI units for a consistent preliminary design check.
Formula Used
This calculator uses a practical screen-loss approach based on gross area, net open area, velocity through the opening, and a loss coefficient tied to open-area ratio.
Agross = width × submerged depth × number of screens
Anet,clean = Agross × φ
Anet,fouled = Agross × φ × (1 − blockage)
Vapproach = Q / Agross
Vnet = Q / Anet
K = 1.45 − 0.45R − R²
R = Anet / Agross
hL = K × Vnet² / (2g)
hdesign = hfouled × (1 + safety factor)
Qmax = Anet,fouled × √[(2g × allowable working headloss) / K]
How to Use This Calculator
- Enter the design flow rate in cubic meters per second.
- Enter the effective screen width and submerged water depth for one screen.
- Add the number of identical screens working in parallel.
- Enter the clean open-area percentage from the screen layout or supplier data.
- Estimate a blockage percentage to reflect expected debris buildup.
- Enter a safety factor and an allowable headloss target.
- Submit the form to view clean, fouled, and design results above the form.
- Use the chart and export buttons to compare results and save output files.
Example Data Table
| Flow (m³/s) | Width (m) | Depth (m) | Screens | Open Area (%) | Blockage (%) | Safety (%) | Allowable Loss (m) | Design Loss (m) | Status |
|---|---|---|---|---|---|---|---|---|---|
| 0.80 | 0.90 | 0.75 | 1 | 45 | 25 | 15 | 0.15 | 0.8560 | CHECK DESIGN |
| 0.35 | 1.20 | 1.10 | 2 | 62 | 20 | 10 | 0.30 | 0.0039 | PASS |
| 1.10 | 1.00 | 0.80 | 1 | 50 | 20 | 10 | 0.20 | 0.7354 | CHECK DESIGN |
Frequently Asked Questions
1. What is screening headloss?
Screening headloss is the energy or water-level drop that occurs when flow passes through bars, openings, or mesh. Smaller openings, higher velocities, and more blockage increase that loss.
2. Why does blockage raise headloss so quickly?
Blockage reduces the effective net area. When the same flow passes through less open area, velocity rises sharply. Since headloss depends on velocity squared, losses can increase very fast.
3. What does open-area percentage mean?
Open-area percentage is the share of gross screen area actually available for flow. It reflects bar thickness, spacing, supports, and screen geometry. Higher open area usually lowers hydraulic loss.
4. Which velocity matters most in the calculation?
Approach velocity is useful for general screening checks, but velocity through the net open area drives the loss equation directly. Fouled net velocity is especially important for conservative design.
5. Can this be used for inclined or special-profile screens?
Yes, for early comparisons and preliminary sizing. However, bar profile, inclination, submerged conditions, and manufacturer-specific performance can change the real loss, so final design should be verified separately.
6. Why include a safety factor?
A safety factor helps cover uncertainty from debris type, uneven clogging, maintenance intervals, fluctuating flow, and simplified assumptions. It makes the design check more conservative and practical.
7. What is maximum recommended flow?
It is an approximate flow limit that keeps the calculated design loss within your allowable threshold under the selected fouled condition. It helps judge whether more area or cleaning frequency is needed.
8. Is this calculator enough for final construction documents?
It is best used for planning, option studies, and preliminary checks. Final documents should also consider structural loading, debris character, maintenance access, upstream control, downstream conditions, and supplier data.