During the operation of the RO reverse osmosis system, a sudden sharp increase in the conductivity of product water and rapid drop in salt rejection rate serve as critical warning signs of equipment malfunction. Unlike the gradual deterioration of water quality caused by natural aging of membrane elements, abrupt conductivity spikes are mostly triggered by sampling errors, pipeline cross-contamination, seal failure, abnormal operating parameters or membrane structural damage. Failure to address such issues in a timely manner will accelerate membrane element wear, result in substandard product water over the long term and push up operation and maintenance costs significantly. Drawing on frontline pure water operation and maintenance experience, this paper sorts out a standardized troubleshooting workflow: rule out false faults first, inspect physical leakage second, verify operating conditions and parameters third, and finally identify membrane damage. It also summarizes seven common types of frequent faults and a complete emergency inspection process, which can be directly applied on site.
I. Seven Most Common Fault Causes & Targeted Quick Solutions
After eliminating instrument malfunctions, the real triggers of sudden conductivity spikes fall into four categories: abnormal sampling and pipelines, unbalanced operating conditions, seal leakage and cross-flow, and irreversible damage to membrane elements. Following the on-site inspection principle of simple first, complex later; frequent faults first, rare faults later, this section sorts out seven typical faults and corresponding solutions to help maintenance staff locate issues rapidly and eliminate defects efficiently.
1. False Over-limit Readings from Testing & Sampling (Top Priority for Inspection, Most Likely Misjudgment)
Fault Cause
This is a false water quality alarm with no actual equipment failure, usually caused by non-standard sampling and testing leading to falsely high readings.
Common issues: dirty sampling containers, stagnant water trapped in product water pipelines, conductivity meter without regular calibration, internal leakage of downstream valves, raw water mixing into the product water pipeline.
Solutions
Use clean sampling containers and fully flush pipelines to drain stagnant water; calibrate conductivity meters on a regular basis; fully inspect product water pipelines and valves to completely eliminate cross-contamination and internal leakage.
2. O-ring Leakage of Membrane Housings (Most Frequent Equipment Fault)
Fault Cause
This is the most prevalent on-site failure. Aging, cracked or damaged O-rings at both ends of membrane housings, or twisted, improperly installed seals during membrane replacement or maintenance will result in raw water bypass. High-salinity raw water without RO filtration mixes directly into product water, causing an immediate sharp surge in product water conductivity.
Solutions
Replace all aged and failed sealing rings; evenly apply silicone-based lubricant during installation to ensure flat and tight sealing. If water quality exceeds standards after membrane replacement, first recheck the sealing installation procedure.
3. Membrane Element Oxidation by Residual Chlorine (Irreversible, Membrane Must Be Scrapped)
Fault Cause
Polyamide RO membranes cannot withstand residual chlorine. If pre-treatment activated carbon fails and is not regenerated or replaced promptly, residual chlorine in feed water will pass through and oxidize the molecular filtration structure of membranes.
Typical symptoms: steep drop in salt rejection rate and abnormally high product water flow. The membrane damage is permanent and irreversible and cannot be restored via chemical cleaning.
Solutions
Immediately replace oxidized and scrapped membrane elements; replace or regenerate activated carbon filter media; continuously monitor RO feed water to guarantee zero residual chlorine and prevent recurrent oxidative damage.
4. Telescope Effect of Membrane Elements (Physical Breakage)
Fault Cause
Frequent equipment startup & shutdown, abrupt pressure fluctuations of high-pressure pumps, excessive product water backpressure will push membrane bags and leaves outward, creating the classic "telescope effect". This leads to physical deformation and structural breakage of membrane elements, with concentrated brine leaking directly into product water and causing sudden substandard water quality.
Solutions
Replace deformed and damaged faulty membrane elements; overhaul check valves and backpressure valves at the product water side to avoid backflow and backpressure during shutdown; standardize operation procedures, stabilize operating pressure and refrain from frequent startup and shutdown.
5. Failed Seals at Membrane End Caps / Central Tubes (Highly Concealed Fault)
Fault Cause
This fault is extremely hidden and easily overlooked. Aging, falling-off or failed built-in seals on membrane central tubes and end caps allow high-salinity concentrated water from the brine side to leak into the product water side, resulting in persistently high product water conductivity.
Solutions
Disassemble and inspect each housing one by one, replace all defective built-in seals and reassemble in line with standard procedures.
6. Severe Fluctuations in Operating Parameters
Fault Cause
Operating parameters deviating from design standards are core triggers of water quality instability:
① Single-stage recovery rate exceeds 75%, causing heavy brine concentration and drastically increased salt ion penetration through membranes;
② Abnormally rising feed water temperature (each 1°C temperature rise boosts membrane salt permeability by 3%~6%);
③ Excessively high or low operating pressure weakens membrane filtration stability and reduces salt rejection efficiency.
Solutions
Strictly control single-stage recovery rate ≤75%; adjust operating pressure seasonally according to feed water temperature; prohibit over-temperature, over-pressure and overload operation.
7. Heavy Scaling & Fouling of Membrane Elements
Fault Cause
Mild scaling and fouling usually only reduce product water flow and raise trans-membrane pressure difference. Long-term lack of maintenance triggers severe concentration polarization, excessive salt accumulation on membrane surfaces and massive salt ion penetration through membrane layers, eventually leading to continuous conductivity rise. Common fouling types include mineral scale, biological slime, organic matter and colloids.
Solutions
Identify fouling types based on pressure difference changes and operating conditions, then perform targeted acid & alkali chemical cleaning. If water quality and salt rejection cannot recover after cleaning, replace the membrane elements directly.
II. Five-Step Rapid Emergency Troubleshooting Procedure
When you detect an abrupt surge in conductivity, do not disassemble membranes, clean or replace them blindly. Follow this standardized 5-step emergency process to pinpoint faults quickly and minimize downtime losses and equipment wear.
1.Emergency shutdown to stop further damage
Turn off the high-pressure pump immediately to halt abnormal operating conditions and prevent irreversible deterioration of membrane elements.
2.Inspect feed water quality
Test residual chlorine, SDI, raw water conductivity and temperature of RO feed water to verify whether the pretreatment system malfunctions.
3.Complete seal inspection
Check all membrane housing ends, pipeline connections and sealing components. Prioritize sealing leakage, the most common failure.
4.Separate sampling per pressure vessel
Collect and test water samples from each pressure vessel individually to accurately identify the faulty housing and narrow down the troubleshooting scope.
5.Review operating conditions
Cross-check recent records of pressure, temperature, recovery rate and operational logs to rule out human error and incorrect parameter adjustments.
III. Core Summary
Practical experience summed up from frontline operation and maintenance: More than 80% of sudden conductivity spikes in RO product water fall into two main categories. Quickly distinguishing fault types can drastically cut down ineffective maintenance work and save costs.
✅ Repairable Faults (Seal Leakage)
Caused by aging or improperly installed sealing rings. Water quality can be fully restored simply by replacing fittings and standardizing installation, featuring low cost and fast repair.
❌ Irreversible Faults (Membrane Oxidation)
Membrane elements damaged by residual chlorine penetration cannot be repaired. Membrane replacement and pretreatment system rectification are mandatory to prevent repeated failures.
Key maintenance tip: Follow the troubleshooting principle of simple tasks first, complex ones later. Prioritize easily fixable issues including sampling errors, seal leakage and abnormal operating parameters, and only confirm irreversible membrane damage at the final stage. This method can restore qualified product water rapidly while keeping maintenance costs under effective control.
