Page 174 - Introduction to Marine Engineering

160 Fuel oils, lubricating oils and their treatment

changeover valves or levers and oil circulation will continue. The
particles of dirt collect on the outside of the strainer element or basket
and can be removed by compressed air or brushing. A strainer should be
cleaned as soon as it is taken out of the system, then reassembled and left
ready for use.
Magnetic strainers are often used in lubricating oil systems, where a
large permanent magnet collects any ferrous particles which are
circulating in the system. The magnet is surrounded by a cage or basket
to simplify cleaning.
Fine filters, again in pairs, are used to remove the smallest particles of
dirt from oil before the oil enters the finely machined engine parts in
either the fuel injection system or the bearings of the rotating
machinery. Fine filters are full-flow units which clean all the oil supplied
to the engine. The filtering substance may be a natural or synthetic
fibrous woollen felt or paper. A felt-type fine filter is shown in Figure
8.5. A steel division plate divides the steel pressure vessel into an upper
and a lower chamber. Dirty oil passes into the upper chamber and
through the filter element, then the filtered oil passes down the central
tube to the lower chamber and out of the unit. A magnetic filter can be

SERVICING INDICATOR LIFTING HANDLES
VENTPLUG

MAGNETIC ELEMENT STEAM HEATING JACKET
MICROFELT 206 CARTRIDGE
FLOW OUT TO IN

DIVISION PLATE

BODY DRAIN
DIFFERENTIAL PRESSURE
CONNECTIONS

Figure 8.5 Fine filter