Efficient combustion in marine engines depends on clean and good-quality fuel oil. However, the heavy fuel oil used onboard ships is rarely pure. It contains contaminants such as water, sludge, and solid particles that can damage engines if not removed.
To ensure fuel quality, ships use a series of purifying equipment—mainly separators (purifiers) and clarifiers—to remove water and impurities before fuel reaches the engine.
1. Gravity Separation – The Basic Method
The simplest method of fuel cleaning is gravity separation.
Because water and solid particles are heavier than fuel, they naturally settle at the bottom of a tank, while clean fuel floats on top. The clean fuel is collected from the upper outlet, and the sludge/water is drained later.
Although simple, gravity separation is slow and inefficient, especially for modern high-capacity engines.
2. Centrifuging – Fast & Efficient Fuel Cleaning
Modern ships use centrifugal separators, which enhance the effect of gravity by rotating the fluid at high speed.
Centrifugal Force Formula
(F = Centrifugal Force , r = Radius , n = RPS)
A centrifuge spins the bowl at thousands of revolutions per minute.
This creates a force much stronger than gravity, pushing heavier contaminants outward while lighter clean fuel remains near the center.
Purifier vs. Clarifier
- Purifier → Separates fuel + water + solids (two-liquid separation)
- Clarifier → Removes solid impurities only (single-liquid separation)
Purifiers also remove some solids, and clarifiers remove small amounts of water, but their primary functions differ.
3. Basic Construction of a Marine Purifier
A typical fuel oil purifier consists of:
Exterior Framework
Cast iron housing that supports the bowl, disks, feed and outlet lines.
Bowl & Disk Stack
- High-tension stainless steel construction
- Disk stack increases separation efficiency
- Bowl may be manual-clean or self-cleaning
Vertical Shaft
Transfers motor power to the rotating bowl using gears or belts.
Horizontal Shaft or Belt Drive
Connects the electric motor to the bowl through:
- Clutch pads
- Drive belt (in some models)
Spiral Gear
Transmits rotation from horizontal to vertical shaft.
Clutch / Friction Pads
Prevents motor overload by allowing smooth acceleration of the heavy bowl.
Attached Gear Pump
Supplies or discharges fuel to/from the purifier (depending on model).
4. How a Purifier Works
Inside a purifier, the mixture of oil, water, and solids is fed into the rotating bowl.
Due to density differences:
- Solids → Move to outermost part of the bowl
- Water → Forms a layer just inside the solids
- Clean Fuel → Remains near the center and exits through clean-oil outlet
A gravity disc controls the fuel-water interface position.
Selecting the correct gravity disc is important and depends on the fuel oil density.
Due to density differences:
5. Sludge Discharge Mechanism (Self-Cleaning Purifiers)
Modern purifiers can remove sludge without stopping the machine.
The system uses hydraulic water to open and close the bowl.
Basic Operation
- Purifier reaches operating speed.
- Water is supplied to create a seal in the bowl.
- Fuel enters and purification begins.
Sludge Discharge Cycle
When sludge discharge starts:
- V1 operates – Oil inlet bypasses the purifier.
- V4 opens briefly – Water enters the bowl to initiate cycle.
- V3 closes – Bowl closing water stops.
- V2 opens – Bowl opening water is supplied.
- Purifier de-sludges – Sludge is ejected and cycle resets.
After discharge, water again seals the bowl and the purifier continues normal operation.
Conclusion
Fuel purification is a critical process to protect marine engines from damage and improve combustion efficiency.
Modern centrifugal purifiers ensure:
- Clean fuel
- Reduced wear and tear
- Improved engine performance
- Efficient removal of water and sludge
Sindhu Marine supplies genuine and OEM spare parts for all major purifier brands used in the marine industry.
For inquiries on purifier spares, discs, bowl parts, or complete unit supplies—
Contact Sindhu Marine FZE for reliable marine solutions.