← Technology WikiRO Membrane (1812 / 3012)
An RO (reverse osmosis) membrane is a semi-permeable composite film that removes dissolved salts, heavy metals, and most contaminants down to 0.0001 microns — the core purification stage of any RO system.
How it works
- Feed water is pressurized (typically 60–100 PSI for residential systems) against the membrane surface.
- Water molecules pass through the 0.0001-micron pores; dissolved solids are rejected and flushed to drain as concentrate.
- Most residential membranes are TFC (thin-film composite) polyamide spiral-wound elements.
- Common sizes: 1812 (1.8"×12") for 50–100 GPD home systems, 3012 (3.0"×12") for 200–800 GPD light-commercial systems.
Key specifications
| Pore size | ≈0.0001 micron |
| Salt rejection (nominal) | ≥96% (NaCl, standard test) |
| 1812 dimensions | 1.8" × 12" (50/75/100 GPD) |
| 3012 dimensions | 3.0" × 12" (200–800 GPD) |
| Typical lifespan | 2–3 years (depends on feed TDS and pre-filtration) |
What buyers and QC should check
- Always protect the membrane with sediment + carbon pre-filters — chlorine kills TFC membranes.
- Ask for the salt-rejection test report, not just the GPD rating; a high-GPD membrane with poor rejection is a bad trade.
- Verify dry vs wet membrane: dry membranes store longer, wet membranes must stay moist.
- For OEM buyers: confirm whether the membrane brand is fixed or substitutable in the BOM.
Free one-page QC checklist (PDF)
The buyer checks from this entry, condensed for the factory floor or the inspection. No signup needed.
Download free PDF checklistCommon questions
How often should an RO membrane be replaced?
Typically every 2–3 years in residential use. The honest signal is filtered-water TDS: when it climbs noticeably above your baseline, the membrane is exhausted — even if it is still producing water.
What is the difference between 1812 and 3012 membranes?
Physical size and flow rate. 1812 (1.8×12 inch) suits 50–100 GPD home systems; 3012 (3×12 inch) suits 200–800 GPD light-commercial or high-flow home systems. They are not interchangeable without the matching housing.
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