"Self-cleaning" does not mean "zero maintenance." That distinction matters, and it is one that most manufacturers avoid discussing directly.
Coanda screens are genuinely self-cleaning for debris. Leaves, branches, algae, sediment, and organic material are continuously swept off the screen face by the high-velocity shearing flow. This self-cleaning mechanism works reliably across thousands of installed screens worldwide. It is not a marketing claim. It is fluid dynamics.
But over years of continuous operation, other processes occur that self-cleaning cannot remove: mineral scale deposition, biological fouling, and gradual capacity reduction from deposits that adhere to the wire surface at the molecular level. These processes are slow (measured in years, not days) but they are real, and they require periodic attention.
This guide is what ADENCO has learned from reviewing screens after 5, 10, and 12+ years in operation. It is an honest account of maintenance: what really happens, how often, and what it costs.
Table of Contents
- The Self-Cleaning Reality
- What Self-Cleaning Does Remove
- What Self-Cleaning Does Not Remove
- The ADENCO Maintenance Schedule
- Capacity Degradation: What to Expect Over Time
- Maintenance Cost Comparison
- When to Contact ADENCO
- Frequently Asked Questions
- References
The Self-Cleaning Reality
Every Coanda screen operates on the same principle: water flows over tilted wedge wire at high velocity, and the shearing force of the flow carries debris across the wire tips and off the screen [1][2]. This works because:
- The wire tilt angle (3°–7°, 5° standard) creates a geometry where debris cannot become lodged in the slot
- The flow velocity across the screen surface (2–3 m/s) provides sufficient drag force to carry particles larger than the slot opening
- The continuous flow means the cleaning action occurs every second the screen operates
This self-cleaning mechanism removes all debris that lies on top of the wire surface: leaves, twigs, branches, algae filaments, sediment particles, plastic fragments, organic material, and aquatic organisms. In our experience across hundreds of installed screens, the self-cleaning function does not degrade over time. A screen that is self-cleaning in year one is equally self-cleaning in year ten.
What changes over time is not the self-cleaning function. It is the condition of the wire surface itself.
What Self-Cleaning Does Remove
Based on observations at operating sites, across ADENCO screens from 1 to 12+ years in operation, the self-cleaning mechanism reliably removes:
-
Autumn leaf fall: the highest debris loading most screens experience. Even in heavily wooded catchments (broadleaf forest directly above the intake), the shearing flow carries leaves off continuously. At the Lodore Falls site in the UK, which takes water from a wooded catchment, the previous wire-basket intake blocked within hours every autumn. The Coanda screen that replaced it operates through every autumn without intervention [3].
-
Storm debris: branches, gravel, and organic material carried during flood events. The screen surface is free of debris within minutes of the flood receding.
-
Algae and aquatic vegetation: filamentous algae and weed fragments are swept off the wire tips. This remains effective even during peak algae blooms in eutrophic (nutrient-rich) water.
-
Sediment: sand, silt, and gravel larger than the slot opening. Published studies from operating sites and laboratories report sediment exclusion of roughly 40 to 80% depending on screen geometry, flow and particle size [4]. The effect depends strongly on particle size: on a 1 mm screen, laboratory tests excluded around 90% of particles coarser than the slot, well under half of those between half-slot and full-slot size, and almost nothing smaller than half the slot width.
-
Ice and snow: under moderate cold conditions (above approximately -14°C), flowing water prevents ice accumulation on the screen surface. Below this threshold, anti-icing measures may be required [5].
What Self-Cleaning Does Not Remove
Three processes occur at the wire surface that the self-cleaning flow cannot remove. These are the real causes of maintenance work on Coanda screens:
1. Mineral Scale Deposition
Water with elevated calcium carbonate (hard water), iron, or manganese content gradually deposits mineral scale on the wire surface. This scale bonds to the stainless steel at the molecular level: it is not lying on the surface where flow can sweep it off. It adheres to the surface [6].
Where we see it: Hard water (>200 mg/L calcium carbonate), groundwater-influenced rivers, and water with pH above 7.5. Iron-rich water (visible orange staining on rocks) and manganese-rich water are also high risk.
What it does: Mineral scale gradually narrows the effective slot width. A 1.0 mm slot with 0.2 mm of mineral scale on each wire surface becomes a 0.6 mm effective slot: reducing flow capacity by approximately 40%. The process is slow (typically measurable over 3–5 years) but cumulative.
How to fix it: Pressure washing or, for heavy mineral scale, a mild acid wash (dilute citric acid or phosphoric acid). See the cleaning procedure below.
2. Biological Fouling (Biofilm)
In warm, nutrient-rich water, a thin biological film develops on the wire surface: a layer of bacteria, algae, and organic compounds. At most sites, the flow velocity keeps biofilm thin enough that it does not significantly affect performance. In some conditions (warm, slow-flowing, nutrient-rich water with long low-flow periods), biofilm can build up to a thickness that reduces slot capacity [7].
Where we see it: Municipal intakes downstream of agricultural runoff, warm-climate sites, and screens that experience extended periods of reduced flow (seasonal operations, drought conditions).
What it does: Biofilm narrows the effective slot width similarly to mineral scale, but it also traps fine sediment particles within its structure, creating a composite deposit that is more difficult to remove than either biofilm or sediment alone.
How to fix it: Pressure washing. Biofilm is mechanically soft and comes off easily under a 100–150 bar pressure wash.
3. Freshwater Mussel and Macro-Organism Colonisation
In some rivers and reservoirs, freshwater mussels, barnacles (in brackish water), or other organisms that attach to surfaces colonise the screen structure: not the wire surface (which is too narrow and constantly swept by the flow) but the support rods, frame components, and weir structure. In extreme cases, mussel growth can encroach on the slot openings from the support rod side.
Where we see it: Warm, calcium-rich freshwater. Rare at cold-climate or soft-water sites.
What it does: If not removed for many years, mussel growth can restrict flow through the support structure and partially block slot openings from below.
How to fix it: Manual removal during the annual inspection. In severe cases, the screen panel can be removed for thorough cleaning.
The ADENCO Maintenance Schedule
Based on operating data from installed screens ranging from 1 to 12+ years in operation, ADENCO recommends the following maintenance schedule:
Annual: Visual Inspection (30–60 minutes)
Inspect the screen for:
- Visible mineral scale deposits: white or grey mineral buildup on wire surfaces
- Biofilm: slimy green or brown coating on wire or support structure
- Mechanical damage: impact marks from flood debris, displaced wires, frame distortion
- Weir condition: erosion, cracking, or debris accumulation on the acceleration plate
- Collection chamber: sediment accumulation, structural condition, condition of the penstock connection
No tools required beyond visual observation. Document condition with photographs for comparison year to year.
Every 2–5 Years: Pressure Wash (2–4 hours)
Pressure wash the screen panel using clean water at 100–150 bar. This removes:
- Accumulated biofilm
- Light mineral scale
- Fine sediment trapped in biofilm matrix
- Algae growth on support structure
Do not exceed 200 bar: excessive pressure can deform thin wedge wire, particularly on narrow-slot (0.5 mm) panels.
Timing: Schedule the pressure wash during a low-demand period. Divert flow during washing (the screen is typically out of service for 1–2 hours).
The interval depends on water chemistry. Clean mountain water: every 5 years is sufficient. Hard water or nutrient-rich water from agricultural catchments: every 2–3 years.
Every 5–10 Years: Chemical Descaling (if required) (4–8 hours)
For screens in hard water or iron/manganese-rich environments where pressure washing alone does not fully restore slot capacity:
- Isolate the screen from the water supply
- Apply dilute acid solution (citric acid (5–10% concentration) or phosphoric acid) to the screen surface using a low-pressure sprayer
- Allow contact time of 30–60 minutes to dissolve the mineral scale
- Rinse thoroughly with clean water at moderate pressure (50–100 bar)
- Inspect slot openings under magnification to confirm that the mineral scale has been removed
- Flush the collection chamber to remove dissolved mineral scale residue
Important: Do not use hydrochloric acid (HCl) on stainless steel: it attacks the passive chromium oxide layer and causes pitting. Citric acid and phosphoric acid are safe for all stainless steel grades used in Coanda screens.
Every 10–15 Years: Condition Assessment
After a decade of operation, ADENCO recommends a formal condition assessment:
- Wire cross-section measurement: to check for corrosion-related material loss (indicates whether the original grade was correctly chosen)
- Slot width verification: to confirm that the slot openings remain within the design tolerance
- Structural integrity: weld condition, support rod attachment, frame straightness
- Capacity test: comparing current throughput to original design capacity under equivalent hydraulic head conditions
If the material grade was correctly matched to the water chemistry, a Coanda screen in good condition at 10 years will continue performing for the rest of its up to 25-year design life. We have screens in operation for more than 12 years with no measurable degradation beyond normal mineral fouling, which routine cleaning removes.
Capacity Degradation: What to Expect Over Time
Based on measurements at operating sites, across screens of varying age and water chemistry (our oldest screens are now past year 12; the later rows are projections consistent with that data):
| Screen Age | Typical Capacity (% of original) | Primary Cause | Action Required |
|---|---|---|---|
| Year 0–2 | 95–100% | None | Annual inspection only |
| Year 2–5 | 85–95% | Light mineral scale, biofilm | Pressure wash restores to 95–100% |
| Year 5–10 | 75–90% | Moderate mineral scale | Pressure wash + acid descale restores to 90–98% |
| Year 10–15 | 70–85% (if uncleaned) | Heavy mineral scale, composite deposits | Acid descale restores to 85–95% |
| Year 15+ | Stable after cleaning | Cleaning cycle maintains capacity | Continue scheduled maintenance |
The critical insight: capacity degradation is not structural deterioration. It is surface fouling that is fully reversible with cleaning. A screen that has been cleaned on schedule retains 90–98% of its original capacity into its second decade. The same screen left uncleaned performs at 70–85%, but a single thorough acid descale restores it to near-original performance.
This is fundamentally different from mechanical screen degradation, where worn chains, corroded sprockets, and fatigued bearings represent permanent structural losses that require component replacement.
Maintenance Cost Comparison
| Maintenance Item | Coanda Screen | Mechanically Cleaned Screen |
|---|---|---|
| Electricity | None | Continuous |
| Routine inspection | 1 visit a year | Weekly to daily |
| Mechanical parts | None | Chains, bearings and motors wear out |
| Pressure washing | Every 2–5 years | Included in mechanical maintenance |
| Chemical descaling | Every 5–10 years, where mineral scale forms | N/A |
| Annual overhaul | None | Yes |
Over a 25-year service life, the maintenance cost of a mechanically cleaned screen adds up year after year, while a Coanda screen needs little more than the annual inspection. This does not include the cost of unplanned downtime from mechanical failures: which is zero for a static screen and a significant risk for mechanical systems.
When to Contact ADENCO
Contact ADENCO engineering support if you observe:
- Visible slot widening: indicates corrosion, suggesting the original material grade may be insufficient for the water chemistry. ADENCO will assess whether a grade upgrade is needed.
- Structural deformation: bent wires, displaced support rods, or frame distortion from flood debris impact. May require panel repair or replacement.
- Capacity below 70% of design after pressure washing and acid descaling: indicates a fouling mechanism beyond normal mineral scale that requires specialist investigation.
- Wire surface pitting: small holes or rough texture on the wire surface, indicating active corrosion. This is a problem of material selection, not of maintenance.
- Any uncertainty about cleaning chemicals, procedures, or equipment. ADENCO provides maintenance guidance specific to your screen's material grade and water chemistry.
Frequently Asked Questions
Do Coanda screens really need zero maintenance?
No, and any manufacturer who claims otherwise is not being honest. Coanda screens are self-cleaning for debris (leaves, branches, sediment, algae), and this self-cleaning function works reliably for the life of the screen. However, mineral scale, biofilm and colonisation by organisms build up over years of operation and need periodic attention. ADENCO's recommended maintenance is: annual visual inspection (30–60 minutes), pressure washing every 2–5 years (2–4 hours), and acid descaling every 5–10 years in hard water (4–8 hours). Total annual maintenance amounts to little more than one inspection a year and an occasional manual clean, against the weekly to daily attention mechanically cleaned screens need.
How often should a Coanda screen be cleaned?
Pressure washing every 2–5 years is sufficient for most sites. The interval depends on water chemistry: clean, soft mountain water may need washing only every 5 years; hard, iron-rich, or nutrient-laden water may require washing every 2–3 years. Acid descaling for heavy mineral scale is needed every 5–10 years in hard water environments. ADENCO can recommend a site-specific schedule based on your water analysis.
What chemicals are safe to use on stainless steel Coanda screens?
Citric acid (5–10% concentration) and phosphoric acid are safe and effective for removing mineral scale from calcium carbonate, iron, and manganese from all stainless steel grades. Never use hydrochloric acid (HCl): it destroys the passive chromium oxide layer and causes pitting corrosion. After any chemical cleaning, rinse thoroughly with clean water at moderate pressure. If unsure, contact ADENCO for grade-specific cleaning guidance.
How long does a Coanda screen last?
With correct material selection for the water chemistry and scheduled maintenance, a Coanda screen has a design life of up to 25 years in clean water; in flood-prone, high-sediment rivers 15 to 20 years is the more realistic expectation; performance declines gradually before the screen stops working. ADENCO has screens in operation for more than 12 years with no structural degradation: only surface fouling that is reversed by routine cleaning. The key to longevity is correct initial material selection: the grade must match the water's chloride concentration, pH, and temperature range. A wrong material choice causes irreversible corrosion; correct material with routine cleaning provides up to 25 years of operation in clean water.
What causes a Coanda screen to lose capacity over time?
Capacity reduction is caused by mineral scale deposition (calcium carbonate, iron, manganese) and biological fouling (biofilm) that gradually narrow the effective slot width. In hard water, a 1.0 mm slot can narrow to 0.6 mm over 5–10 years, reducing capacity by approximately 40%. This is not structural damage: it is surface fouling that is fully reversible with pressure washing and acid descaling. A properly maintained screen operates at 90–98% of original capacity indefinitely.
Can I do Coanda screen maintenance myself?
Yes. Annual inspection requires only visual observation and photographs. Pressure washing requires a standard commercial pressure washer (100–150 bar): the same equipment used for building and vehicle cleaning. Acid descaling requires citric acid solution, a low-pressure sprayer, and standard personal protective equipment (gloves, eye protection). No specialist tools or training are needed for routine maintenance. ADENCO provides a maintenance guide with every screen it delivers, and our engineering team is available by phone or email for questions.
References
-
Wahl, T.L. (2003). Design Guidance for Coanda-Effect Screens. U.S. Bureau of Reclamation, Research Report R-2003-03. Denver, CO.
-
Wahl, T.L. (2001). "Hydraulic Performance of Coanda-Effect Screens." Journal of Hydraulic Engineering, Vol 127, No 6. ASCE.
-
"The Coanda Effect." International Water Power & Dam Construction Magazine. Retrieved April 2026, from http://www.waterpowermagazine.com/features/featurethe-coanda-effect/
-
"Sediment Exclusion from Water Systems Using a Coanda Effect Device." International Journal of Hydraulic Engineering, Vol 4, No 2, 2015.
-
"Performance of Coanda-Effect Screens in a Cold Climate." Journal of Cold Regions Engineering, Vol 28, No 4, ASCE, 2014.
-
"Common Intake Screen Clogging Causes & Coanda Screen Solutions." Johnson Wedge Wire. Retrieved April 2026, from https://www.johnsonwedgewire.com/news/intake-screen-coanda-wedge-wire-solution.html
-
"Why Intake Screen Cleaning Is Critical for Industrial Water Systems." Ocean Marine Contracting. Retrieved April 2026, from https://www.oceanmarinecontracting.com/why-intake-screen-cleaning-is-critical-for-industrial-water-systems/
-
Wahl, T.L. (2004). "Coanda Screen Field Applications." Water O&M Bulletin, Vol 208. U.S. Bureau of Reclamation.
-
"Guide on Stainless Steel Wedge Wire Screen Panel Cleaning." Wedge Wire Screen. Retrieved April 2026, from https://www.wedgewire-screen.com/technology/wedge-wire-screen-panel-cleaning.html
Published by ADENCO: Advanced Engineering Coanda Intake Screens. We build screens with a design life of up to 25 years, and we tell you exactly what it takes to keep them performing. Every ADENCO screen is delivered with a site-specific maintenance guide. Questions about your screen's maintenance? Contact our engineering team →