Marine Installation Manual
2021-08
4-70
4 Ancillary Systems
4.6 Fuel oil system
X72DF
Fuel oil filters — Arrangement ‘A’
Filtration grading
The grade of filter mesh is relative to the size of particles it captures, however,
there are different ratings for filtration efficiencies and the rating parameters vary
among manufacturers.
For simplicity, it is assumed that particles are spherical, therefore the size is de
-
fined by an equivalent diameter. A filter’s grading size is associated with this
equivalent diameter but can vary depending on whether an
absolute
or
nominal
grading system is used.
Figure 4
-
41 Mesh size difference between absolute and nominal
Absolute Filtration Grade
This value indicates the largest equivalent diameter capable of passing through
the filter. This value equals the size of the mesh coarseness and can therefore be
referred to as the
absolute sphere passing mesh size
. Approximately all particles
larger than the specified size will be trapped on or within the filter.
Nominal Filtration Grade
This value is typically smaller than the absolute value and refers to an equivalent
diameter where most particles will be trapped. Generally, this is interpreted as a
85% to 90 % filtration for particles larger than the nominal value but this can
range (from 60 % to 90 % approximately). Because of the complication this vari
-
ation can cause, the nominal grade for filtration is not used in the following.
Arrangement ‘A’ of fuel oil filters (see
) comprises:
•
An automatic self-cleaning filter of maximum 10
m abs., installed either in
the 'cold' feed system (see
) or in the 'hot' booster system
close to engine inlet (see
).
•
A duplex filter of recommended maximum 25
m abs., installed down
-
stream of the engine inlet booster system (see
).
NOTE
WinGD provides all filter mesh sizes in absolute (abs.) values.
D
Absolute
Nominal
SM-0528
D
