3030226 Rev. D 6-10 Troubleshooting
6.13 Low Percent Rejection
The overall membrane performance can be affected by a number of factors. Poor
rejection performance, as well as, high TDS/µS can result from fouled membrane, low
pump pressure, inadequate waste flow, or RO feed water problems. The recommended
first step for any ‘membrane performance’ question is to confirm the rejection
percentage and product TDS/µS with a hand-held meter. If the product water quality is
poor, investigate the membrane. However, if the water quality tests ‘normal’,
investigate the monitoring circuits.
1. Disinfectant or cleaner left in RO.
a. Check for presence of disinfectant or cleaner; rinse as necessary.
2. Waste flow too low.
a. Check for obstruction or kink in waste line.
3. Product flow too high.
a. See Section 6.11.
4. Membrane scaled or fouled.
a. Verify condition of softener pretreatment equipment.
b. See membrane cleaning procedure in this manual.
5. Erroneous meter readout.
a. Verify water quality with independent meter and check conductivity probe
connection.
6. Membrane failure.
a. Replace membrane.
7. Change in RO feed water TDS/µS.
a. Verify RO feed and product water quality with independent meter.
b. Softener problem, rinsing out high levels of salt.
8. Normal membrane rejection decline (over time).
a. Perform AAMI / CSA water lab analysis.
b. Replace membrane if indicated by analysis.
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