Troubleshoot RWO OWS System
Oil-water separators (OWS) are essential equipment for ships that need to comply with the International Convention for the Prevention of Pollution from Ships (MARPOL). OWS systems separate oil from water and discharge the water overboard, while retaining the oil for proper disposal. However, OWS systems can malfunction due to various reasons, such as sensor failure, wiring errors, or using non-original spare parts. In this blog post, we will share a real-life example of how to troubleshoot and calibrate an OWS system using the SKIT/S -DEB 5.0 / OMD-24 model.
The SKIT/S -DEB 5.0 / OMD-24 is a type-approved OWS system that uses a capacitive measuring cell to detect oil content in water. The measuring cell consists of a sensor electrode and a reference electrode, which are connected to an electronic unit that displays the oil content in parts per million (ppm). The system also has a coalescer and a polisher, which are filters that remove oil droplets from the water before discharging it overboard.
The case we will discuss is from a ship that the ship's engineer reported that the system was showing a sensor failure alarm, which meant that the system could not measure the oil content accurately. The customer engaged a 3rd party service station in another port to check the system, but due to their limited understanding of the equipment, they are unable to resolve the problem and recommended a qualified service station to troubleshoot the system.
Our RWO trained service engineer visited the ship in Singapore and found several deficiencies beside the sensor failure:
* Firstly, he found that the sensor failure was caused by the sensor electrode being a non-original part, which had a different capacitance value than the original one. He dismantled the sensor electrode and replaced it with an original part, which rectified the sensor failure. This is probably the number 1 cause of sensor failure.
* He found that the wiring connection from the OMD-24 unit to the RWO panel was incorrect, which could interfere with the signal transmission. He rewired the connection and rectified the wiring error.
* He found that the OMD certificate from the last calibration was for a different unit and the current OMD does not have any commissioning report or calibration record. So, he proceeds to calibrate the OMD-24 unit using clean water and two check fluids with known oil content (2 ppm and 7 ppm). He verified that the unit displayed the correct oil content values for each test.
* He conducted a functional test of the OWS system in the presence of the ship's engineer and confirmed that the system was working properly and complying with the MARPOL regulations.
* He found that the on-board spare parts for the coalescer and polisher were not original, which could reduce their efficiency and lifespan. He strongly recommended to order and replace them with original spare parts as soon as possible to prevent future problems with the OWS system.
This case illustrates how important it is to use original spare parts and follow proper wiring instructions when installing and maintaining an OWS system. It also shows how a professional service engineer can troubleshoot and calibrate an OWS system using standard procedures and tools. By doing so, you can ensure that your OWS system is always in good condition and compliant with environmental regulations.
Related: RWO OWS fault codes explained, and which spare parts to order
N&P Maritime has been RWO GmbH's Singapore partner since 2016, supplying genuine RWO spare parts and genuine Deckma OMD parts sourced through RWO. Since October 2025 we are a supply-only company and do not provide onboard service.
N&P Maritime keeps stock of common RWO/Deckma consumable spare parts in Singapore, such as coalescer filters, adsorber polishers, zinc anodes, gauges and desiccators.
We reply to quotation requests within 1 business day and deliver in-stock parts within 3 business days. There is no minimum order requirement.
Contact us at sales@npmarine.sg and/or +65 97684033 if you have any questions.
*RWO GmbH has been supplying future-proof made in Germany solutions for marine water treatment for over 45 years. Their product portfolio includes equipment for the treatment of drinking and process water as well as systems for pollution prevention such as oily water separators or sewage treatment plants. RWO is a technological leader in the field of oil/water-separation with over 16,000 units delivered worldwide. More than 40 global sales and service stations.
FAQ
What causes a sensor failure alarm on an RWO OWS system?
A non-original sensor electrode is likely the number one cause of sensor failure on an RWO OWS system. In the case described, the non-original electrode had a different capacitance value from the original, causing the alarm; replacing it with an original part rectified the failure. Incorrect wiring can also interfere with signal transmission.
How do I calibrate an OMD-24 after a sensor failure or missing calibration record?
Calibrate the OMD-24 using clean water and two check fluids with known oil content of 2 ppm and 7 ppm. Then verify the unit displays the correct oil content for each test. In the case described, the previous OMD certificate was for a different unit, and the current OMD had no commissioning report or calibration record.
Can wrong wiring from the OMD-24 to the RWO panel cause OWS signal problems?
Yes. Incorrect wiring from the OMD-24 unit to the RWO panel can interfere with signal transmission. In the case described, the service engineer found the connection was incorrect, rewired it and rectified the wiring error. Proper wiring is therefore important when installing and maintaining an OWS system.
Why should I replace non-original coalescer and polisher spares on an RWO OWS?
Non-original coalescer and polisher spares can reduce efficiency and lifespan, and the engineer strongly recommended ordering and replacing them with original spare parts to prevent future OWS problems. In the case described, the on-board spares were not original. Genuine RWO consumables are available from N&P Maritime, a supply-only company.
Where can I get genuine RWO OWS and Deckma OMD spare parts in Singapore?
N&P Maritime is RWO GmbH's Singapore partner since 2016 and supplies genuine RWO OWS parts and Deckma OMD parts sourced through RWO. It is supply-only and does not provide installation, repairs, onboard attendance or lifeboat services. Quotation requests are answered within 1 business day, and in-stock parts are delivered within 3 business days.