Marine Installation Manual
2022-03
4-70
4 Ancillary Systems
4.7 Fuel oil system
X62DF-S2.0
Pressure regulating valve
The pressure regulating valve returns the excess fuel oil that is not required by the
main engine, recirculating more when the engine is at lower power. To avoid
heating-up of the fuel by recirculation, the return pipe is designed with cooling
ribs.
It also works to ensure that the pressure downstream of the low-pressure feed
pump remains 1bar above the evaporation pressure of the water and there pre
-
vents entrained water within the fuel oil system from flashing off into steam.
The pressure regulating valve should have a flat steady-state characteristic across
the fuel oil recirculation flow range.
Mixing unit
The mixing unit equalises the temperature between the hotter fuel oil returning
from the engine and the colder fuel oil from the service tank. The temperature
difference between these sources is particularly high when changing over from
HFO to MDO/MGO and vice versa.
Due to the small amount of fuel consumed, especially in part-load operation,
only a small mixing unit is required. It is recommended that the tank contains no
more than approx. 100 litres. This is to avoid the changeover from HFO to
MDO/MGO or vice versa taking too long.
Type
Self-operated or pilot-operated, with a manual emergency
control. Either direct hydraulically or pneumatically
actuated. However, when using a pneumatically actuated
valve, use a combined spring type to close the valve in case
of air supply failure.
Maximum capacity
: Refer to feed pump capacity.
Minimum capacity
Approx. 20% of that of the fuel oil feed pump
Service pressure
Max. 10bar
Pressure setting range
2-6bar
Inlet pressure change
The inlet pressure may vary by up to 0.8bar depending on
the flow in the range of 20% to 100%.
Working temperature
Below 100°C
Fuel oil viscosity
Depending on the fuel oil system’s heat control, viscosity at
working temperature will often differ. It will not be more than
100cSt, however can be considerably less (as low as 2cSt
with lower viscosity fuel like MDO/MGO or possibly LSHFO,
see viscosity-temperature diagram -
).
The manufacturer's specification must comply with the fuel
viscosity range. For system options with additional tempera
-
ture regulation, see
