Fuel Supply Unit


Product: Fuel Supply Unit

MAR-IN-CONTROL pre-fabricated, tailor-made Fuel Supply Units are used to prepare Heavy Fuel oil (H.F.O) for the Diesel Engine. The H.F.O. is brought to the required viscosity, temperature, pressure and cleanliness.
Applying the fuel supply unit offers the possibility to run the engine of a ship on H.F.O. instead of Marine Diesel Oil (M.D.O.), which gives a considerable cut-down in fuel costs.

The Fuel Supply Unit is designed according to the customer's demands, taking into account the type of vessel and engine and the layout of the engine room.
The figure shows the flow diagram of a typical Fuel Supply Unit, which has been applied several times. It offers the following possibilities: 1 main engine can be connected. The engine can run on MDO or HFO.

Módulos de combustible
The shown Fuel Supply contains the following components: 

1.- 1 Double filter for the HFO
On this filter, also a differential pressure alarm is installed. In case the filter is clogged, an alarm will be generated, whereafter a manual switchover should be made.

2.- 2 Feeder pumps
Two screw pumps for HFO and MDO, of which one is always running, while the other pump is standby. In case of a failure of the running pump, the standby-pump will take over.

3.- 1 Pressure control system
This system comprises a pneumatic pressure controller, a 2-way pneumatic operated valve and an air filter/regulator. The system pressure can be regulated with this system.

4.- 1 Fuel flow meter system
This system comprises the flow meter itself, a differential pressure alarm and a bypass valve, which will be opened automatically in case of flow meter blockage.

5.- 1 Degassing tank

6.- 3 Level switches
For level control and low level alarm of the degassing tank.

7.- 1 Spring loaded valve
To prevent pressure drop in the degassing tank during degassing.

8.-. 1 Degassing valve
This valve is automatically operated.

9.- 2 Booster pumps (Circulation pumps) return to graphic
Two screw pumps for HFO and MDO. One pump is running while the other one is stand-by.

10.- 2 Steam heaters
The temperature, and therefore the viscosity of the HFO is controlled with these heaters.

11.- 1 Viscotrol, viscosity control system, pneumatic version. This system comprises:
    - Viscosity sensor with differential pressure transmitter and thermometer
    - Viscosity indicating controller (VIC)
    - Control valve for saturated steam
    - Viscosity alarm switch for low and high viscosity alarm (Va)
    - Air filter / regulator
    - P/I converter, for a read-out of the actual viscosity on the bridge.

12.- 2 Pressure alarm switches
To generate a low pressure alarm, and as signal for switching-over from the running pump to the stand-by pump.

13.- 1 Temperature alarm switch
To generate a high temperature alarm.

14.- 2 Pressure gauges
To monitor the outlet pressure of the pumps.

15.- 1 Automatic filters for HFO
This filter is installed downstream of the booster pump unit. It is a self-cleaning filter, using compressed air.

16.- 1 Accumulator
To prevent pressure drop in the fuel outlet line during flushing of the automatic filter.

17.- 1 Electric control box, comprising:   
    -Main switch
    - Overload protections for the electric motors
    - Alarm indicating lamps for all alarms.
    - Switches for the electric motors for pumps and the viscosity sensor.
    - PLC circuitry for automatic switchover of pumps and for generation of alarms.
    - Alarm output contacts for connection possibility to the ship's alarm system.

  The Fuel Supply Unit is prefabricated, built up on a skid. This is shown in figure 2



The HFO is transported from the day tank through the double filter by the double feeder pump unit.

In case the filter is clogged and thus prevents a free flow of HFO, a differential pressure alarm unit will generate an alarm. This is indicated on the control panel, wherefore a switchover to the bypass filter should be made. The clogged filter can then be cleaned while the unit is operating.

The pressure after the feederpump is monitored by a pressure switch; in case the pressure drops, there probably is a malfunction of the operating feederpump. An alarm is generated and in the control box the automatic switch-over to the standby feederpump is accomplished.

Parallel to the feeder pump unit, the pressure control system is installed; the pressure controller will open the pneumatic operated valve, releasing some of the pressure built up by the feeder pump, with increasing pressure and viceversa. As the controller is provided with Proportional and Integral action, the system pressure can be regulated accurately.

The flow meter at the pressure side of the feeder pump measures the total amount of HFO used. If required, this flow meter can be equipped with an impulse transmitter and amplifier for connection to the ship's computer or a remote counter. In case the flow meter is clogged or defective and blocks the passage of HFO, an alarm will be generated by the differential pressure contact installed. The bypass valve parallel to the meter will then be opened, allowing the system to operate on HFO.

After the flow meter, the HFO enters the degassing tank. Level switches are installed to control the level in the tank. If the level decreases beneath a certain point, the degassing valve on top of the tank will be opened. The degassing will increase the level of the fuel in the tank. However, if the level is too low and degassing does not solve this, a low-level alarm will be generated.

The booster pumps lets the HFO circulate through the heaters, the self-cleaning filter unit and the Viscotrol to the engines. These pumps are provided with the same switchover device as the feeder pumps.

After the booster pumps, the steam heaters are installed. The amount of saturated steam, flowing through the heaters is regulated by the Viscotrol viscosity control system. The fuel is brought to the required injection viscosity. A pneumatic alarm switch is used to indicate, if the viscosity is within its expected values; an alarm is generated in case of a too low or too high viscosity.

The actual viscosity of the fuel can be read from the scale of the viscosity-indicating controller. Also, the P/I converter generates an electronic signal from the pneumatic viscosity signal, so the viscosity can be read-out or recorded on the bridge. A thermometer is mounted on the Viscotrol house, which offers the possibility to monitor the temperature.

The return flow of HFO from the engines is brought into the degassing tank (which also has the function of mixing tank). The cold HFO coming from the day-tank is mixed with this returned hot HFO. With a return line to the day-tank, the heat of the returning HFO would be lost energy.

Optional features

The fuel supply units can be supplied with the following features:

· Nozzle cooling circuit

At the suction side of the twin nozzle-cooling pump a thermostatic 3-way mixing valve is installed. This valve has a temperature bulb, with which the temperature in the nozzle cooling line is measured. The two input ports of the valve are connected to the return line of MDO (hot oil coming from the engines) and to the day-tank (MDO at ambient temperature) via a double filter.

The mixing valve will regulate itself, creating a mixture with an approximate temperature of 68º C. This mixture is pumped through the nozzles of the engines by the double nozzle cooling pump unit.


The MDO-circuit is provided with a single pre-filter, a MDO-pump and a double end filter. The MDO-pump automatically starts in case of a critical alarm of the Fuel Supply Unit (when it is impossible to operate in HFO) and when starting up.

Switchover valves for auxiliary engines

If more than one (auxiliary) engine is connected to the Fuel Supply Unit, each engine can be provided with two switchover valves. So, each engine can run on MDO or HFO, independent from the other engines. The electric control box controls the valves.

In case of a critical alarm the valves are automatically switches over to the MDO-position (and the MDO-pump is started).


The Mar-in Controls Fuel Supply Unit offers several advantages:

  • Pre-fabricated, built on a skid. The unit is easy to install in an engine room.
  • All (flange) connections to be made by the shipyard can be made at the edge of the skid.
  • Taylor-made: The unit can be re-designed to comply with the customer's requests.
  • Adjustment of the output parameters (pressure, viscosity) of the fuel is easy to accomplish.
  • Automatic switchover of pumps and self-cleaning filter and, in case of a critical alarm, switch-over to MDO, warranty a continuous operation of the unit.
  • Output (critical) alarm contacts for remote indication or connection to the ship's computer.