1. Reading model codes
Every manufacturer names things differently, but the code carries only four kinds of information: size, water type, energy class and special function.
| Code fragment | Meaning | Examples |
|---|---|---|
| 4040 / 8040 | Element diameter × length in inches: 4 in × 40 in, 8 in × 40 in | ESPA2-4040, BW30-400 |
| 365 / 400 / 440 | Active membrane area in ft²; in the same envelope, more area means more permeate per element | CPA5 MAX 440 |
| BW | Brackish Water — brackish and surface water | BW30-400, BW 400 R |
| SW / SWC | Seawater desalination | SW30HRLE-400, SWC6 MAX |
| ULP / LP / ESPA | Ultra-low or low pressure: less pressure for the same permeate flow | ULP22-8040, ESPA2-LD |
| LE / XLE / HRLE | Low Energy / Extra Low Energy / High Rejection Low Energy | BW30HRLE-440, XLE-440 |
| HR / XHR | High Rejection, usually at a higher operating pressure | SW30XHR-400, TBW-400XHR |
| FR / LFC | Fouling Resistant / Low Fouling — modified, less fouling-prone surface | BW30FR-400/34, LFC3-LD |
| LD | Low Differential pressure — wider feed spacer | ESPA2-LD, CPA5-LD |
| -i / IG | Vendor-specific markers such as iLEC interlocking end caps or industrial grade packaging | BW30HRLE-440i |
Read a code in this order: size first, then water type and energy class, then whether you need fouling resistance or low pressure drop. For area and rejection of a specific element, see the parameter library.
2. Series positioning across brands
| Position | Ovay | Hydranautics | DuPont (FilmTec) | Toray | LG | CSM | Vontron |
|---|---|---|---|---|---|---|---|
| Ultra-low energy | OV-U-8040-440 / OV-X-8040 | ESPA1 / ESPA2 | BW30HRLE / XLE | SUL-G20 | BW 400 ES | RE8040-UL | ULP32 |
| Standard brackish | OV-L-8040 400 / 440 | CPA3 / CPA5 | BW30 PRO-400 | TM720D-400 | BW 400 R | RE8040-BE | LP22-8040 |
| High rejection | OP5-10 (99.8%) / OP5-30 MAX | CPA7 MAX | BW30XHR PRO | TM720D (99.8%) | BW 400 R G2 | RE8040-BEHR | PURO-II |
| Fouling resistant | OV-FR-8040 400 / OV-FR-8040-LE | LFC3-LD | BW30FR / Fortilife | TLF / TBW | BW 400 AFR | RE8040-BLF | FR22-8040 |
| Seawater | OV-SW-8040-XHR / HR 400 | SWC6 / SWC6 MAX | SW30HRLE / SW30XHR | TM820A / TM820V | SW 400 GR / ES | — (not in library) | SW8040HR |
| Nanofiltration | — (not in library) | ESNA1-LF | NF90 / NF270 | NF series | NF 400 | NE8040-40 | — |
This table shows position within each manufacturer; it does not mean elements from different manufacturers are interchangeable. Even with the same area and rejection, pressure-drop behaviour and temperature correction can differ. Ovay entries follow the library's OV-U / OV-X / OV-L / OV-FR / OV-SW and OP5 tiers.
3. Four-step selection
Step 1: let the water decide the series
Clean groundwater and RO permeate: low-energy series first. Surface water and reuse: fouling-resistant series. Salinity above 10000 mg/L or seawater: seawater elements only. When you need selective removal of divalent ions or organics, consider nanofiltration.
Step 2: let recovery and temperature decide the area
Calculate total area first, then convert to element count. Watch the cold case: at 10 °C flux is roughly 60% of the 25 °C value, so a design selected only at 25 °C will fall short in winter.
Step 3: check pressure drop and spacer
With high feed salinity, a large concentration factor, or many elements in series per stage (6 or more), prefer LD (low pressure drop) models — otherwise the tail-stage pressure drop exceeds the limit and shows up as "enough pressure but not enough permeate".
Step 4: check cleaning and replacement strategy
Where fouling load is high, the value of a fouling-resistant element is not in its initial numbers but in the cleaning interval. If you clean monthly, the flux assumption or the pretreatment is wrong — changing the model is only a secondary fix.
4. Choosing by application
| Application | Prefer | Why |
|---|---|---|
| Municipal tap water to pure water | Low or ultra-low pressure brackish elements | Stable quality; lowest energy and capex |
| Groundwater (high hardness) | Brackish element + softening or antiscalant | Scaling risk dominates over fouling |
| Surface / river water | Fouling-resistant element + UF pretreatment | High organic and colloidal load |
| Municipal wastewater reuse | Fouling-resistant element, low flux design | COD and microbial risk; long cleaning interval needed |
| Seawater desalination | Seawater element (high rejection, high pressure) | High osmotic pressure; first-pass recovery only 40–45% |
| Boiler make-up / ultrapure water | High-rejection brackish element + EDI | TOC and weak electrolytes must be controlled |
| Food / pharmaceutical | Sanitary elements, heat-sanitisable models | Hygienic certification and cleaning validation |
5. Five common traps
- Looking at rejection and not at flux. A 99.7% element with low flux needs higher pressure for the same permeate flow, so both energy and capex rise.
- Swapping 400 ft² for 440 ft² without changing the array. More area shifts the permeate and concentrate split per element, and the tail concentrate flow may become insufficient.
- Mixing models of the same size. Different pressure-drop characteristics inside one vessel cause uneven flow distribution, and after months of operation the fouling differs visibly.
- Treating a "low-pressure element" as a "low-energy system". System energy also depends on recovery, pump efficiency and whether there is interstage boosting; the element is only one factor.
- Ignoring vendor software versions. Parameters for the same model can shift between yearly datasheets — cite the source version when quoting figures in a tender.
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