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RO membranes — elements and replacements
RO Membranes and Spiral-Wound Elements in India
RO membranes are spiral-wound elements that reject dissolved salts from a pressurised feed, typically at 96 to 99.8 percent for sodium chloride. They are specified by element size, feed TDS band, fouling risk and required rejection. Element diameter and length must match the pressure vessel bore, adapters and brine seals exactly.
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Answer first
What RO Membranes Are, and How They Are Specified
RO membranes are spiral-wound elements that reject dissolved salts from a pressurised feed, typically at 96 to 99.8 percent for sodium chloride. They are specified by element size, feed TDS band, fouling risk and required rejection. Element diameter and length must match the pressure vessel bore, adapters and brine seals exactly.
An RO element is chosen from four variables, and only one of them is the size printed on the label. Feed TDS sets the rejection class, fouling load sets whether a fouling-resistant construction is needed, energy priority decides whether a low-energy element pays for itself, and plant flow decides between 4040 and 8040.
Replacement is where most enquiries in this group start. If you are replacing an existing element, send the model designation you are removing together with the operating pressure, feed TDS and recovery — an equivalent is matched on active area, rejection and pressure rating, not on the part number.
Choose a type
RO Membranes by Type
Each type below has its own page with a full specification table, selection guidance and its own enquiry route.
Brackish Water RO Membranes
Brackish water RO membranes are spiral-wound elements applied to feed water up to roughly 10,000 ppm TDS, operating at 10 to 17 bar with sodium chloride rejection of 96 to 99.7 percent.
Seawater RO Membranes
Seawater RO membranes are high-rejection spiral-wound elements applied to feed of 25,000 to 45,000 ppm TDS, operating at 55 to 70 bar with sodium chloride rejection of 99.4 to 99.8 percent.
Fouling Resistant RO Membranes
Fouling resistant RO membranes are elements built with a wider feed spacer and a lower-charge, smoother membrane surface so that organic and biological foulants are less likely to adhere and easier to clean off.
Low Energy RO Membranes
Low energy RO membranes deliver comparable salt rejection at a lower applied pressure, typically 7 to 11 bar against the 10 to 17 bar a standard brackish element needs.
4040 RO Membranes
A 4040 RO membrane is a spiral-wound element four inches in diameter and forty inches long.
8040 RO Membranes
An 8040 RO membrane is a spiral-wound element eight inches in diameter and forty inches long, carrying roughly four times the active area of a 4040.
Specification
Element types at a glance
| Element type | Feed TDS band | Typical NaCl rejection | Typical applied pressure | Chosen for |
|---|---|---|---|---|
| Brackish water (BW) | Up to 10,000 ppm | 96–99.7 % | 10–17 bar | Borewell and municipal feed — the default class |
| Seawater (SW) | 25,000–45,000 ppm | 99.4–99.8 % | 55–70 bar | Seawater and very high salinity feed |
| Fouling resistant (FR) | Variable, treated effluent | 99.0–99.6 % | 10–17 bar | High organic and biological load, STP and ETP recycle |
| Low energy (LE) | Below about 2,000 ppm | 98.5–99.4 % | 7–11 bar | Continuously running plants on low-TDS feed |
| High rejection (XLE / high area) | 500–10,000 ppm | 99.5–99.8 % | 12–17 bar | Where permeate quality drives the specification |
Brackish water (BW)
- Feed TDS band
- Up to 10,000 ppm
- Typical NaCl rejection
- 96–99.7 %
- Typical applied pressure
- 10–17 bar
- Chosen for
- Borewell and municipal feed — the default class
Seawater (SW)
- Feed TDS band
- 25,000–45,000 ppm
- Typical NaCl rejection
- 99.4–99.8 %
- Typical applied pressure
- 55–70 bar
- Chosen for
- Seawater and very high salinity feed
Fouling resistant (FR)
- Feed TDS band
- Variable, treated effluent
- Typical NaCl rejection
- 99.0–99.6 %
- Typical applied pressure
- 10–17 bar
- Chosen for
- High organic and biological load, STP and ETP recycle
Low energy (LE)
- Feed TDS band
- Below about 2,000 ppm
- Typical NaCl rejection
- 98.5–99.4 %
- Typical applied pressure
- 7–11 bar
- Chosen for
- Continuously running plants on low-TDS feed
High rejection (XLE / high area)
- Feed TDS band
- 500–10,000 ppm
- Typical NaCl rejection
- 99.5–99.8 %
- Typical applied pressure
- 12–17 bar
- Chosen for
- Where permeate quality drives the specification
Bands are typical published ranges across the element classes. Rejection, area and pressure rating are confirmed against the datasheet of the element quoted.
Selection guidance
The rule that decides 4040 against 8040
It is a plant-flow decision, not a quality decision. An 8040 element carries roughly four times the active area of a 4040 of the same length, so an 8040 array reaches a given permeate flow with about a quarter of the elements and a quarter of the vessels. That is fewer connections, fewer seals and less to go wrong.
4040 earns its place where plant room space is tight, where the plant is small enough that an 8040 vessel would be oversized, or where staged expansion matters more than element count. Below roughly 5 m³/h the 4040 usually wins on practicality; above it the 8040 usually wins on cost per litre.
What you cannot do is mix sizes within an array. Vessel bore, adapters and brine seals are all size-specific, so a size change is a vessel change.
Application mapping
Where RO Membranes Are Used
Borewell and brackish groundwater
- Typical requirement
- 2,000–10,000 ppm feed at 55–70 % recovery
- Indicated configuration
- Brackish-water elements, frequently two-stage, with antiscalant selected from concentrate saturation
STP and ETP recycle
- Typical requirement
- Variable treated effluent with high organic load
- Indicated configuration
- Fouling-resistant elements behind a UF or MBR barrier
Seawater desalination
- Typical requirement
- 25,000–45,000 ppm at 35–45 % recovery
- Indicated configuration
- Seawater elements with a dedicated high-pressure pump and matching vessel class
Pharmaceutical and process pre-treatment
- Typical requirement
- Low-TDS feed ahead of EDI or mixed bed
- Indicated configuration
- High-rejection or low-energy elements sized for continuous duty
Commercial terms
How This Category Is Quoted
Water treatment does not have a list price, and any supplier quoting one before seeing a feed analysis is quoting a different plant from the one you need.
Pricing basis
On request, and capacity-dependent. Plant pricing moves with capacity, feed water analysis and the recovery target; membranes, cartridges and resins are quoted per element, per lot or per litre of media.
Order quantity
From a single replacement element or a case of cartridges through to full plant scope. Consumable lines are quoted per box or per lot, and the lot size is stated on the quotation.
Lead time
Confirmed per line item at quotation stage. Stocked consumable lines and made-to-order plant differ substantially, so a single blanket lead time for the category would be misleading — the quotation carries the figure for each line.
Invoicing
GST invoice against company or institutional purchase order. Proforma issued where advance payment or internal approval requires it.
Delivery coverage
Despatch from Delhi NCR across India, including plant, project and institutional sites. Delivery city and site access are asked for at enquiry because both affect despatch mode.
Documentation
Technical datasheet for the item quoted, and a test certificate where the principal supplies one with that product. Tender and institutional documentation formats are prepared on request — send the format with the enquiry so the quotation is issued in a form you can submit without rework.
Request for quotation
Request a Quote — RO Membranes
Fields marked with an asterisk are required. The technical fields are what usually decide whether you get a quotation on the first pass or three emails of clarification.
Frequently asked
RO Membranes — Common Questions
How long does an RO membrane last?
Typically three to five years on brackish feed and two to three years on treated effluent, but age is the weakest predictor. Replace on trend rather than on date.
The standard trigger is a 10 to 15 percent rise in normalised salt passage, or a 10 to 15 percent fall in normalised permeate flow, measured against commissioning data and not recovering after a clean.
Can I replace one element in a vessel instead of the whole set?
You can, and it is sometimes the right call when a single element has failed through a seal or a mechanical fault. It is usually the wrong call when the whole array has aged together.
Mixing a new element with elements at the end of their life shifts flow onto the new one, which loads it harder than design. Where the array is uniformly aged, replacing the set gives more predictable performance.
What damages an RO membrane permanently?
Free chlorine is the main one. Polyamide membranes are oxidised by chlorine and the damage cannot be reversed by cleaning, so carbon or SMBS dosing ahead of the RO is part of the scope rather than an accessory.
Beyond chlorine, running dry, hydraulic shock at start-up, and leaving elements wet and stagnant during a shutdown all cause damage that a clean will not recover.
Do I need to state the brand when ordering RO membranes?
Not necessarily. If your BOQ names an element, quote it to us and we quote against it. If it does not, we usually offer more than one option so the technical and commercial comparison stays with you.
For equivalents, send the model you are replacing plus operating pressure, feed TDS and recovery. The match is made on active area, rejection and pressure rating.
Related Products and Categories
Specified alongside ro membranes, and the category this page sits in.
Pressure vessels these elements fitCartridge filters that protect themIndustrial RO systems built around themBack to Water Purification Systems
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