Pressure drops, permeate conductivity spikes or a sudden loss of flow are threats to product quality, downstream equipment and your shift’s KPI targets. At Membracon, we know that in these moments, you need a clear-headed technical triage. This guide uses structured diagnostics to help you quickly stabilise your Reverse Osmosis (RO) and Ultrafiltration (UF) systems, then shows you how to prevent these alarms from recurring.

 

Immediate Triage – Diagnosing Common RO & UF System Alarms

Low-Pressure Alarms on Your Reverse Osmosis Membrane

A low-pressure fault on the RO feed side usually indicates that the high-pressure pump is starved or that the membrane is no longer offering the expected resistance. Follow this triage sequence before resuming automatic operation.

Step-by-step checks:

 

• Verify pre-filter condition – Isolate and inspect cartridge or media pre-filters. A blinded pre-filter chokes feed flow and causes immediate inlet pressure collapse. Replace elements if the differential pressure exceeds 0.5–0.7 bar over the clean condition.
• Check feed water supply and valves – Confirm that all manual isolation valves between the break tank and the pump suction are fully open. A partially closed valve or a stuck float in the break tank can simulate a system fault.
• Confirm pump rotation and amp draw – For three-phase pumps, a phase reversal will let the pump run but produce no real pressure. Measure motor amps against the nameplate. Low amps with high noise suggest air locking or cavitation.
• Assess membrane condition – If pre-filters and feed side are healthy, but the high-pressure pump outlet pressure remains low even with the concentrate valve throttled, the reverse osmosis membrane may be mechanically compromised. Element telescoping or severe scaling can create internal bypass paths, dropping inlet resistance. In this case, a destructive dissection of the lead element is the only definitive check.
• Sensor and transducer integrity – Cross-check the panel reading with a calibrated analogue gauge at the pressure vessel. A faulty transducer can trigger a false alarm and mask a perfectly normal operating condition.

 

Conductivity Spikes and Permeate Quality Drops on the RO Water Membrane

If your permeate quality has suddenly degraded, assume a barrier breach until proven otherwise, then investigate membrane scaling or surface fouling. Isolating the vessel and performing individual element probing is the quickest route to the root cause.

A rising conductivity trend that accelerates over hours, or a step change that coincides with a recent maintenance event, points to different failure modes. Use the following logical sequence.

 

• Rule out instrumentation error – Flush the conductivity cell, check temperature compensation and calibrate with a known standard. Data logging systems often mask a simple probe drift.
• Interconnector and O-ring integrity – The most common cause of a sudden permeate quality failure on a RO water membrane is a dislodged, rolled, or chemically-degraded interconnector O-ring between elements within a pressure vessel. If you have just performed a cleaning or membrane replacement, a pinched O-ring will let concentrate bleed straight into the permeate tube. Isolate individual vessels and compare permeate conductivity. A single vessel showing many times the conductivity of its neighbours has an internal seal failure. Open the vessel and inspect O-rings under magnification.
• Membrane telescoping or glue-line crack – In an older system, hydraulic shock (water hammer) can physically shift membrane layers, cracking the glue lines. This is irreversible. A vessel profile test using vacuum decay or a conductivity probe inserted into the permeate tube at various depths can localise the damaged element. Replace the suspect element immediately.
• Surface scaling and concentration polarisation – If the drift is gradual rather than a step-change, take a sample of the last element’s concentrate and check for supersaturation of sparingly soluble salts (silica, calcium sulphate, barium sulphate). Calculate the scaling indices. Increasing concentrate flow or temporarily reducing recovery will lower the local concentration at the membrane surface and confirm whether scaling is depressing rejection.

 

Ultrafiltration (UF) System Flow Rate Drops

A UF system that loses permeate flow without a change in feed quality is almost always dealing with fouling or an imbalance in the backwash sequence. Trans-membrane pressure (TMP) is your key diagnostic parameter – monitor it per train.

Diagnostic approach:

 

• Check TMP trend against the clean baseline – If TMP has risen by more than 0.3–0.5 bar while flux is falling, the hollow fibres are loaded with foulant. A normalised permeability decline of >25% demands chemical intervention.
• Verify backwash and air scour – Confirm the backwash pump is delivering the design flux and that the air scour compressor is achieving rated volume and pressure. Incomplete or shortened backwash cycles often stem from a partially open pneumatic valve or a timer fault in the PLC sequence.
• Feed water upset – Sudden organic or colloidal load from upstream processes (e.g. an overspill from a carbon filter) will blind UF pores. Check the turbidity and colour of the feed. If feed conditions have changed, increase the frequency of chemically enhanced backwashes (CEB) until the source normalises.
• Integrity test – A pressure-decay test (PDT) will detect a fibre break. If fibre integrity is lost, permeate quality (turbidity or SDI) will also degrade, so correlate flow loss with filtrate quality data.

 

What Operators Need to Know

What is a major problem with reverse osmosis?

The primary operational threat to any RO system is membrane fouling (the accumulation of biological slime, scale, or colloidal material on the feed spacer and membrane surface). Uncontrolled fouling forces higher feed pressures, increases energy consumption and reduces both permeate flow and quality, often leading to unplanned shutdowns.

Fouling takes many forms. Biological fouling thrives when pretreatment fails to control bacteria – even chlorinated water can carry nutrients that support downstream growth after dechlorination. Inorganic scaling from calcium carbonate, calcium sulphate or silica precipitates when the solubility limits are exceeded in the concentrate channel. Colloidal fouling, from fine clay, silt, or corrosion products, packs tightly into the first elements and is difficult to reverse once established. The sequence is vicious – fouling raises differential pressure, creating isolated high-velocity zones that further concentrate foulants, accelerating the damage. Early detection through normalised data trending (normalised permeate flow, salt passage and differential pressure) is the only reliable defence.

 

What cannot be removed by reverse osmosis?

RO membranes remove 95–99% of dissolved salts and virtually all suspended solids, but they do not effectively reject dissolved gases such as carbon dioxide (CO₂), oxygen and chlorine. Many volatile organic compounds (VOCs) with low molecular weight also pass through the polyamide barrier unless specifically targeted with additional adsorption or degasification steps.

Dissolved CO₂ is particularly problematic because it passes freely through the membrane, re-equilibrating in the permeate and forming carbonic acid, which increases permeate conductivity and undermines the validity of your conductivity-based rejection calculations. This is why mixed-bed ion exchange or membrane degasification is often used after a double-pass RO in high-purity water applications. Chlorine, too, is a small neutral molecule that passes through. Because it also destroys polyamide membranes, a robust dechlorination step (sodium bisulphite dosing or activated carbon) is mandatory before the RO elements. For VOC removal, RO is ineffective against compounds such as trihalomethanes (THMs) and certain solvents, necessitating granular activated carbon or air stripping in series.

 

Moving from Reactive to Preventative Maintenance

The Importance of a CIP cleaning service for UF NF RO systems

A standard maintenance flush can only displace loose deposits from the feed-concentrate channel – it cannot dissolve scale crystals or strip biofilm from the membrane surface. A chemical Clean-In-Place (CIP) service is engineered to restore membrane flux and salt rejection by circulating tailored cleaning chemistries at controlled temperature, pH and flow rate through the elements.

A well-designed CIP programme attacks specific foulants in the right order. For UF NF RO systems, a typical sequence might begin with an alkaline surfactant cleaner to lift organic films and biofoulants, followed by a low-pH acid wash to dissolve carbonate and metal oxide scales. Nanofiltration (NF) elements, with their tighter surface charges, are especially sensitive to irreversible organic fouling and require carefully matched cleaning conditions. The difference between a generic flush and a full CIP is between recovering 10% of lost flow and 95%. At Membracon, our CIP protocols are built around membrane manufacturer guidelines, with full data logging of differential pressure, pH and temperature throughout the recirculation cycle. After cleaning, we map the normalised performance against the original factory baseline to demonstrate recovery.

An outsourced CIP cleaning service becomes essential when in-house teams lack the chemical-handling equipment, the experience to customise the cleaning recipe, or simply the bandwidth to respond as production pressures mount.

 

Booking UF system servicing and maintenance in the UK

Your UF or RO system does not have to carry a Membracon badge for us to support it. Our field service engineers routinely work on legacy plants, containerised systems from other OEMs and multi-technology water treatment lines across the UK. UF system servicing and maintenance in the UK is one of our core offerings, covering scheduled preventive maintenance to emergency call-outs.

A typical UF maintenance visit includes fibre integrity testing, optimisation of the cleaning sequence, replacement of worn pneumatic seals, calibration of transmitters and a thorough assessment of the pretreatment upstream. For RO and NF systems, we offer vibration analysis of high-pressure pumps, element probing and chemical condition audits of feed water. The goal is to build a life-cycle maintenance plan that replaces assets predictably. With a national team of experienced water treatment engineers, Membracon provides the rapid response and deep technical expertise that critical production sites demand.

 

Partner with Membracon for Uninterrupted Production

Membracon has spent over 23 years engineering, servicing and optimising advanced filtration systems for industries that cannot afford downtime. Our UK-based engineers carry the chemicals, spares and diagnostic tools to stabilise your plant in the field, then work with you to design a preventative maintenance schedule that stops problems before they start.

Request an Emergency System Audit or Speak to a Maintenance Engineer Today