July 03rd, 2025

A Marine Engineer's Guide to Oil Purifier Operation

For any marine engineer, the centrifugal oil purifier is one of the most critical pieces of machinery in the engine room. Proper operation of purifiers for fuel oil and lube oil is essential for protecting the main and auxiliary engines from damage. This practical guide covers the fundamental principles, operational best practices, and common troubleshooting tips to help you keep your purifiers running efficiently.

Safety First Disclaimer: This guide is for educational and informational purposes only and is based on general maritime best practices. It is not a substitute for official manufacturer training or the most current version of the equipment's operational manual. Always refer to the official documentation and follow all established safety protocols on your vessel before performing any maintenance or operation.

The Core Principle: How Centrifugal Separation Works

At its heart, a purifier is a high-speed centrifuge that separates liquids and solids based on their different densities. For this to work, the liquids must not be emulsified. When contaminated oil enters the rapidly spinning bowl, the immense G-force (centrifugal force) separates the components:

• Solids (Sludge): The heaviest particles, like dirt, rust, and cat fines, are thrown to the outermost wall of the purifier bowl.
• Water: Being heavier than oil, water forms the next layer inside the sludge.
• Clean Oil: The lightest component, the purified oil, forms the innermost layer.

The magic happens within the disc stack, a large number of conical discs stacked on top of each other. These discs create a massive surface area and very narrow passages, which greatly accelerates the separation process.

Key Operational Modes on Modern Vessels

Shipboard purifiers can be operated in different configurations depending on the need.

• Single Mode: One purifier is used to treat a type of oil (e.g., HFO or Lube Oil). This is the most common setup.
• Parallel Mode: Two purifiers run in single mode simultaneously, treating the same type of oil from the same tank to increase the overall flow rate.
• Series Mode: Two purifiers are run in sequence for HFO treatment, which is recommended when the fuel has a high concentration of solids. The first purifier (the "purifier") removes most of the water and some solids, and the second (the "clarifier") removes the remaining finer solid particles.

Understanding the Gravity Disk (Regulating Ring)

The correct selection of the gravity disk, also known as a regulating ring, is critical for efficient purification. This ring acts like a dam, controlling the oil-water interface inside the bowl.

• If the ring is too wide (large inner diameter): The oil-water interface moves too far outwards. The result is that oil may be lost along with the water discharge.
• If the ring is too narrow (small inner diameter): The interface moves too far inwards. The result is that water will contaminate the clean oil discharge.

The correct size is determined using a nomogram chart based on the oil's density and separation temperature. A general rule of thumb is to use a narrower ring for heavier oil and a wider ring for lighter oil.

Common Troubleshooting Scenarios

Even with perfect setup, issues can arise. Here are some common problems and potential causes.

Problem: Excessive Bowl Vibration or Unbalance

• Incorrect Assembly: Check that all alignment marks ("0" marks) on the bowl parts are perfectly in line. Ensure no parts are missing or that parts from different bowls have been mixed up. [
• Sludge Buildup: An incomplete de-sludging process can leave uneven sludge deposits, causing unbalance. Ensure the ejection cycle is functioning correctly.
• Worn Bearings: Worn or improperly fitted spindle bearings can cause significant vibration. Bearings should always be replaced in pairs and fitted according to the manufacturer's instructions.

Problem: Inefficient Separation (Water in Oil or Oil in Water)

• Incorrect Gravity Disk: This is the most common cause. Verify that the correct size is installed for the oil's density and temperature.
• Wrong Temperature: The oil temperature must be correct to achieve the right viscosity for separation. Check the pre-heater and temperature controllers.
• Low Flow Rate: An incorrect flow rate can affect separation efficiency. Check the feed pump and look for blockages in strainers.

---

Frequently Asked Questions

What is the difference between a purifier and a clarifier?

A purifier separates two liquids (like oil and water) while simultaneously removing solids. A clarifier is designed primarily to remove solid particles from a single liquid. In series operation, the purifier runs first, followed by the clarifier.

What is the purpose of the Centripetal Pump?

The centripetal pump is a stationary device inside the purifier that "peels" the separated liquid (clean oil and/or water) from the rotating bowl and discharges it under pressure. This eliminates foam and allows the liquid to be pumped to the next stage without a separate pump.

Why is the de-sludging (ejection) process necessary?

During separation, heavy sludge and impurities collect at the bowl's wall. The de-sludging process uses operating water pressure to hydraulically open ports in the bowl, ejecting the accumulated sludge into a sludge tank. This self-cleaning action allows the purifier to operate continuously for long periods.