Introduction
When the display panel on your RWO Oily Water Separator shows a fault or alarm message, the clock starts ticking. Your vessel needs to resume bilge water discharge in compliance with MARPOL Annex I, keeping your 15 ppm bilge separator MARPOL compliant, and your team needs to know exactly what the message means, what caused it, and which part —if any — needs to be replaced.
This guide covers every fault and alarm message listed in the official RWO operating manual for the SKIT/S-DEBSPS 1.8, their likely causes, the recommended remedies, and the specific genuine RWO spare parts to order — from bilge water separator spare parts to control components.
All information in this guide is sourced directly from the RWO Operating Instructions for Oily Water Separator System SKIT/S-DEB SPS 1.8, 12th print run, Revision 24.02.2017. Page and section references are included throughout so you can verify each point against your own copy of the manual.
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Understanding the SKIT/S-DEB control display
The RWO SKIT/S-DEB is controlled by a PLC-based unit with a 2-line, 20-character backlit LCD display (§9.5, p.27).It shows system status, operating modes, warnings, and fault conditions in plain text — in English or German, depending on how it was configured at commissioning (§9.6d, p.31).
The display operates in two modes: normal operating mode (showing system state) and fault/alarm mode, where special alarm messages alternate with the status display (§9.6b, p.28). When an alarm is active, the Red LED (Failure) illuminates and the fault message appear cyclically on the display (§9.3b, p.26).
Normal operating mode — display states
📖Manual ref: §9.6b, pp.28–29; Table 3 (Meaning of Indicators), p.19
| Display Text | LED Colour | Meaning |
|---|---|---|
| OPERATION STOP / STAND BY | — | Selector switch in Zero (0) position. System in standby. |
| OPERATION HAND / STAND BY | — | Manual mode selected; system in standby, no bilge level input. |
| OPERATION AUTO / STAND BY | — | Automatic mode; waiting for bilge level to trigger operation. |
| OPERATION [HAND/AUTO] / WATER DISCHARGE | Green | Oil separation in progress. Cleaned water is being discharged overboard. |
| OPERATION [HAND/AUTO] / OIL DISCHARGE | Red | Oil discharge cycle active. Oil directed to collector tank. Pump and heater off. Valve 4 and 15 are open. |
| OPERATION [HAND/AUTO] / FLUSHING | Orange | Coalescer backflush in progress. Pump and heater off. Valves 5 and 15 open. |
| OPERATION [HAND/AUTO] / WATER PASS ADSORBER | Green | Water passing through adsorber stage (units with adsorber fitted only). |
Important: The OMD ALARM state is triggered by the Deckma Hamburg bilge alarm monitor (a 15ppm oil content monitor), not the OWS control unit itself. Both systems must be functioning correctly for MARPOL Annex I compliance (§4.4, p.15).
Complete fault reference table
The table below is a complete reproduction of the RWO fault table (Table 5, §8.2, pp.23–25) with remedies and spare parts information added. Faults are grouped by system area for easier reference. Parts highlighted in green indicate a genuine spare part is recommended.
📖Manual ref: Source: RWO Operating Manual §8.2 Table 5, pp.23–25
| Fault / Display Message | Reason | Remedy | Parts to Order |
|---|---|---|---|
| A — Pump & Flow Faults (Manual §8.2, Table 5, p.23–24) | |||
| Permanent repetition of flushing — short intervals | System drawing air from empty bilge; level switch in bilge not switching off | Switch off the system. Check the level switch. | No part required |
| Permanent repetition of flushing + mano-vacuum shows insufficient suction height | Air leak in suction line or at oil separator (cover, flanges, valves) | Lift off system and suction line. Locate and remove leakage. | No part required |
| Low pump capacity + high vacuum reading | Suction line or rough filter at inlet blocked | Clean suction line and/or rough filter. | No part required |
| Valve closed in suction direction | Open valves. | No part required | |
| Insufficient pump capacity; several metres pressure difference between vacuum meters at pump and separator cover | Coalescer packing is jammed | Flush manually by pressing the 'Test' button. If unsuccessful, remove and replace coalescer. | ✦ Coalescer (item 34) |
| Motor protection switch triggers | Motor burnt out | Replace motor. | ✦ Motor (specify pump model) |
| Short circuit in supply line or motor | Check motor and supply line. | No part required | |
| Motor protection switch set too low | Adjust motor protection relay to motor value. | No part required | |
| Rotor of pump blocked | Determine cause. Remove stator; replace stator and rotor if necessary. | ✦ AEP pump stator + rotor (specify pump model) | |
| Pump shaft blocked | Loosen stuffing box packing. | No part required | |
| B — Valve & Sequencing Faults (Manual §8.2, Table 5, p.24–25) | |||
| Piston valves do not operate | Control air failure | Check compressed air supply (6–8 bar required). | No part required |
| No control voltage present | Check automatic control system — see commissioning checklist §5.5. | No part required | |
| Piston ring defective | Check upper part of piston valve. | No part required | |
| Contamination in solenoid valve | Remove contamination from solenoid valve. | No part required | |
| Solenoid valve defective | Check solenoid valve by switching main switch on/off — you should feel and hear operation. Replace if defective. | ✦ Solenoid valve 24V AC (item 23.3 or 58.3 — check voltage before ordering) | |
| Piston is jammed | Make piston movable. | No part required | |
| System flushes permanently or unusually long | Non-return valve at oil separator inlet does not close | Check, remove and clean non-return valve if necessary. | No part required |
| Oil outlet jammed | Check and clean oil outlet pipeline if necessary. | No part required | |
| Flushing water pressure insufficient | Check flushing water pressure. Flow pressure must be 1 bar (max. 1.5 bar). | ✦ Check flushing water inlet supply | |
| System does not flush | Flushing water outlet (item 5) to bilge blocked | Clear pipeline. | No part required |
| Piston valves (item 5 and/or 15) do not operate | Check connection voltage in control box: 24V DC must be applied between terminals X1-11/12 and X1-13/14. If not, replace PCB. | ✦ PCB / control board | |
| C — Oil Detection Faults (Manual §8.2, Table 5, p.24–25) | |||
| System detects oil but discharges water | Cable connection between control box and electrode interrupted | Check cable connection; replace if necessary. | No part required |
| Electrode clotted | Clean contact surfaces of electrode rods. | No part required | |
| PCB defective | Bridge terminals X2-1 and X2-3 unless water is detected (LED green = water OK). If water still not detected, replace PCB. | ✦ PCB / control board (item PLC, Article No. SPSPOL201675) | |
| System detects oil but does not discharge | Outlet pipeline to oil collector tank blocked | Check pipeline to collector tank; clean if necessary. | No part required |
| Flushing water supply interrupted | Ensure water supply to flushing water inlet. | ✦ Check flushing water supply | |
| Piston valve (item 4 and/or 15) does not operate | Check connection voltage in control box: 24V DC must be between terminals X1-9/10 and X1-11/12. If not, replace PCB. | ✦ PCB / control board | |
| System detects no oil | Electric connection between sensor electrode and PCB defective | Check electric connection. | No part required |
| PCB defective | Check PCB by pulling plug from electrode (item 9). If no oil detection occurs after plug removal, replace PCB. | ✦ PCB / control board | |
| Electric conductivity in oil phase too high — possible emulsion | Avoid emulsion generation. Use separation-friendly cleaning agents in engine room. | No part required | |
| Oil binds water (hygroscopic oil) | [VERIFY] — Consult RWO for advice on hygroscopic oil conditions. Capacitive probe option may be required. | No part required | |
| D — Heater & Power Faults (Manual §8.2, Table 5, p.25) | |||
| No heater power | Heating element defective | Replace heating element. | ✦ Heating element (item 10) — confirm heating element voltage |
| Cable connection interrupted | Check cable connection; replace if necessary. | No part required | |
| Thermo sensor out of tune or defective | Set thermo sensor to 45°C or replace it. | ✦ Thermal sensor / thermostat | |
| Heater contactor defective | Replace contactor. | ✦ Contactor for heater (item 2K2, Art. No. CECRGU321719) | |
| No control voltage present | Transformer fuse defective — unless 24V DC present at terminals X1-7/8 | Replace fuse (1F2, M6.3A). If fault recurs, determine root cause. | ✦ Transformer fuse M6.3A (item 1F2, Art. No. 51311063M1) |
| Cable connection interrupted | Replace cable connection. | No part required | |
| PCB defective | Check PCB. In RED-OIL-DISCHARGE state, 24V DC must be present between terminals X2-9/10 and X2-13/14. If not, replace PCB. | ✦ PCB / control board (CPU-board, Art. No. SPSPOL201675) | |
Alarm display messages — what they mean
In addition to the fault conditions above, the SKIT/S-DEB control unit displays a set of specific alarm messages on the LCD (§9.6b, p.29). These appear alternating with the normal status display when an alarm state is active. The Red (Failure) LED illuminates whenever any alarm is pending.
📖Manual ref: Source: RWO Operating Manual §9.6b, p.29
| Display Message | Meaning | What to Do |
|---|---|---|
LONG TIME RUNNING ALARM | System has been running longer than the set maximum bilge processing time. Suction of air suspected. | Search for cause — likely a leak in the suction line. Switch off and inspect. |
BILGE LEVEL LOW | Upper bilge level switch signal absent; system cannot start or has stopped automatically. | Check bilge level. Check level switch wiring and function. |
REMOTE STOP | Remote stop signal received at terminals X2-5/X2-6. | Check remote stop switch or emergency stop wiring. |
OILTANK OVERFLOW | Oil collector tank level switch (terminals X2-7/X2-8) has triggered overflow alarm. | Empty the oil collector tank before resuming operation. |
MOTOR FAILURE — OVER CURRENT | Motor protection switch has triggered due to overcurrent. | Check motor and supply line. Adjust motor protection relay to motor value. |
SEPARATOR OIL-ALARM | Oil sensor electrode (item 9) has detected oil and triggered discharge cycle, but the system has not cleared. | Check sensor electrode and oil discharge valve operation. |
DIFFERENTIAL HIGH PRESSURE | Pressure difference between upstream and downstream of adsorber exceeds maximum (optional pressure difference switch, terminals X2-11/X2-12). | Reset selector switch to '0'. Check and replace adsorber elements if pressure difference exceeds 2.8 bar. |
SEPARATOR RUN DRY | Dry run protection triggered (optional, terminals X2-13/X2-14). | Check bilge level and suction line for air ingress. |
OIL-SENSOR FAILURE | Fault in oil sensor electrode signal. | Check electrode wiring and electrode (item 9). Replace if necessary. |
BILGE-SENSOR FAILURE | Fault in bilge level sensor signal. | Check bilge level switch wiring. Replace switch if defective. |
The spare parts most commonly needed after a fault
Based on the fault patterns in themanual, the following spare parts are most frequently required. Keeping a basicset of these on board can dramatically reduce vessel downtime.
📖Manual ref: Source: RWO Operating Manual Chapter 12 (Spare Parts), pp.38–44
1. Coalescer filter (item 34) + adsorber elements (items 101, 103)
These are the two filtration consumables at the heart of the SKIT/S-DEB. The oily water separator coalescer filter handles first-stage oil-water separation; the RWO adsorber cartridge elements (activated carbon, 20" and 10") handle second-stage polishing. Both have a finite service life. Replace when OMD alarm persists after calibration, or when pressure difference across the coalescer exceeds 0.2bar (§6.1, p.22) or across the adsorber exceeds 2.8 bar.
Only genuine RWO coalescers should be used for RWO coalescer filter replacement. Non-genuine coalescers allow oil to pass through prematurely, activating the 15-ppm bilge alarm even with a recently replaced filter.
2. Sensor electrode R1" (item 9)
The three-rod capacitance electrode (§9.7a, p.34) functions as the OWS sensor that measures the accumulated oil level in the separator. It must have the correct capacitance value to work with the PCB. Non-genuine electrodes — even those that look identical — often have different capacitance and will trigger an OIL-SENSOR FAILURE alarm. Annual cleaning and inspection is specified in §6.3 (p.22).
3. AEP eccentric spiral pump internals — stator, rotor, stuffing box packing
The AEP pump (item 14) draws bilge fluid through the separator. Stator and rotor wear is normal over time; stuffing box packing can dry out after extended idle periods and cause insufficient suction. RWO supplies these in matched sets. Specify the correct AEP size (AEP1 through AEP6) when ordering. On restart after a long stand still, manually turn the pump shaft before starting (§5.1.7, p.17).
4. Solenoid valves — 24V AC (items 23.3, 58.3)
The SKIT/S-DEB uses multiple RWO solenoid valves for marine OWS operation — controlling the oil discharge cycle (item 4), flushing water inlet (item 15), flushing water outlet (item 5), and adsorber bypass (item 58). Solenoid valve failures are a common cause of sequence faults and ‘piston valves do not operate’ faults. Note: the operating voltage is variable — always check and confirm voltage before ordering (§12.1, p.38).
5. Heating element (item 10)
The heating element assists oil separation by warming bilge water in the separator to the 45°C setpoint. The spare parts list (Table 6a, p.38) specifies a 440V variant. Confirm your vessel's supply voltage before ordering. The thermal sensor set point and heater contactor (item 2K2) should also be checked before replacing the element.
6. PCB / control board (CPU-board, item PLC, Art. No. 5120101050)
The PCB controls oil detection, sequencing, and alarm outputs. Failures are less frequent than consumable items but affect multiple functions simultaneously. If electrode replacement does not resolve an oil detection fault, or if control voltage faults persist after fuse and wiring checks, RWO PCB board replacement is the next step. Article number from Table 7 (p.40): SPSPOL201675.
7. Transformer fuse M6.3A (item 1F2, Art. No. 51311063M1)
A blown transformer fuse is one of the causes of 'No control voltage present'. This is a straight-forward replacement item. If the fuse blows again after replacement, identify the root cause before replacing again. Article number from Table 7 (p.40): 51311063M1.
Recommended maintenance spares — based on RWO manual schedule
📖Manual ref: Source: RWO Operating Manual §6 Maintenance, p.22
The RWO manual specifies the following minimum inspection and maintenance schedule. N&P Maritime, RWO GmbH's Singapore partner since 2016, can supply a consolidated annual spares package.
Regular inspections (§6.1, p.22)
• Check pressure difference across coalescer (max. 0.2 bar) — flush coalescer if exceeded; replace if flushing fails
• Check pressure difference across adsorber (max. 2.8 bar) — replace adsorber elements if exceeded
• Check stuffing box packing on pump — slight leakage (1–2 drops/min) is acceptable; re-tighten or replace if more
• Check suction vacuum at pump suction gauge — inspect stator and rotor if insufficient
Semi-annual inspections (§6.2, p.22)
• Check and replace zinc anode (item 41) if necessary
• Check gear motor oil level; top up if required
Annual inspections (§6.3, p.22)
• Open inspection port —check for sludge deposits; clean if necessary
• Check inner coating —mend damaged spots
• Check seals and piston valves — replace damaged seals and components
• Check and clean sensor electrode (item 9) — replace if necessary
• Check heater element (item 10) function — replace if necessary
• Deckma OMD-24 calibration checks at each IOPP renewal — Deckma Hamburg measuring cells available from N&P Maritime Singapore.
Need genuine RWO parts or a quotation within 1 business day?
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