Separate the safety function from primary solids removal
The cartridge normally sits at the end of pretreatment, near the high-pressure pump. It catches accidental particles and provides a final physical barrier. If it continuously receives the solids an upstream process should remove, high consumption and frequent changes become a process issue rather than simply a spare-parts purchasing issue.
The FilmTec manual commonly recommends 5 µm absolute as a safety-filtration reference and considers finer grades for particular risks. This manufacturer guidance is not a complete specification for every feedwater. The installed membrane requirements and a feed assessment determine the appropriate scope.
Compare retention ratings on the same basis
A nominal grade should not automatically be treated as equivalent to an absolute grade with the same number. Request the test method, retention efficiency and service conditions. Also review fibres, binders, seals and the housing: all must suit the water, chemicals, temperature and pressure.
The housing must prevent flow bypassing the cartridge. Confirm length, end adapters and sealing before approving an alternative replacement. Finer filter media cannot correct a missing gasket, a poorly seated cartridge or a housing arrangement that allows untreated water directly to the outlet.
| Purchasing input | Request | Reason |
|---|---|---|
| Retention | Absolute/nominal rating and test | Avoid false equivalence |
| Hydraulics | Curve and flow per cartridge | Control pressure loss |
| Installation | Seals, ends and length | Prevent bypass |
| Materials | Documented compatibility | Avoid degradation and contamination |
Size for all the water passing through the filter
Use RO feed flow rather than permeate flow alone. In an ideal example, a plant producing 10 m³/h at 75% recovery needs 10/0.75 = 13.33 m³/h of feed. Cartridge area and quantity must accommodate that flow and the characteristics of the incoming water.
Request clean-filter pressure-drop curves and the assembly’s replacement limits. Measure pressure before and after the housing and compare trends at similar flow. Low differential pressure does not establish integrity: bypass or a ruptured cartridge can also give a low reading while protection has been lost.
Treat used cartridges as process evidence
Record replacement date, treated volume, pressure drop and cartridge appearance. Red deposits, gelatinous material or sand suggest questions, but identifying the deposit requires analysis. Compare changes with rainfall, valve operations, regeneration, dosing and carryover of carbon fines or coagulant.
When replacement intervals shorten, investigate the cause before simply adding more cartridges. The answer may involve upstream filtration, improved carryover control or operating changes. Compare cost per volume of feed and train availability, as well as the purchase price of each cartridge and the labour needed to replace it.
Common questions
Does a 1 µm cartridge remove dissolved salts?
No. Particle retention is different from desalination. Dissolved salts need an appropriate separation process such as RO or NF, selected for the duty.
Is high pressure drop the only replacement trigger?
Not necessarily. Manufacturer service limits, hygiene, elapsed time and incidents also matter. The operating plan should define the full replacement criteria.