Crankcase ventilation is an
inconspicuous but technically innovative
separation method to lower engine
emissions. We have to look at the inside
of the engine to understand how
crankcase ventilation works. During the
combustion cycle leakage between the
piston rings and liners causes
combustion gases to enter the crankcase.
These gases which come from the
combustion process have a composition
similar to exhaust gas they are called
blow-by gases. In the crankcase the blow-by gas is enriched with oil this gas is
not eco-friendly but still has to be
continually removed from the crankcase
to prevent an inadmissible rise in
pressure. In the simplest case, this
removal is made via an opening in the
crankcase. However, this method results in
a continual loss of engine oil and is no
longer environmentally acceptable as a
solution. A better solution is to remove
the blow-by gas via an extraction point
on the engine, such as via the rocker
cover and ventilate the crankcase using
a highly efficient oil separator. The
separator can be operated as an open
system where the cleaned blow by gases
returns to the ambient air.
A state-of-the-art feature is the closed
crankcase ventilation system (CCV) where
blow-by gases are recirculated to the
engine air intake to return to the
combustion process. The oil separator
exploits the principle of coalescence to
separate the oil. As blow-by gases pass
through the medium small oil droplets
collect on the fibers of the separation
medium, grow and then exit the filter in
drops on the outlet site where they're
returned to the oil sump.
The cleaned blow-by gases are then
returned to the engine air intake and
sucked in again by the engine. With
closed crankcase ventilation there is a
hydraulic connection between the engine
air intake and the crankcase. Therefore
the constantly changing pressure
difference between the air intake and
crankcase must be compensated for by
pressure regulation to ensure the
pressure level is suitable for the
crankcase. Due to the adjustment of the
pressure in the oil sump the oil
recirculation usually takes place below
the oil sump. The oil column in the
drainage pipe then prevents a bypass via
the drainage pipe to the air intake. If
this is not possible or not desired the
oil recirculation can optionally be made
above the oil level. In this case
Mann + Hummel offers a valve for fitting in the drainage pipe which will prevent this bypass.
As a further option Mann + Hummel 
offers a pressure relief valve
for a number of crankcase ventilation
systems which prevents inadmissable high
crankcase pressure in the event 
that the engine fails.
The servicing of the oil separator could
not be easier. The crankcase is opened
without tools then the separation
element is replaced according to the
specifications of the engine
manufacturer.
