Man V12-1800, Installation Instructions Manual

Page: 45 / 92

Exhaust system
43
Exhaust silencing
Exhaust silencing can be achieved either by
means of an exhaust outlet below the water line or
by installing exhaust silencers.
Exhaust outlet below water line
As well as noise damping, an exhaust outlet below
the water line normally gives rise to an increase in
exhaust backpressure.
A flow−optimised configuration of the exhaust
outlet can reduce this effect.
However, there must be no incidence of vacuum
pressure here.
Caution:
A vacuum at the exhaust outlet leads to
impermissible high turbocharger rpms and
is therefore not allowed.
If the exhaust outlet is located below the water
line, incorporate a bypass to the exhaust pipe with
an outlet above the water line.
If this bypass is omitted, there can be a build−up of
pressure in the exhaust system when the ship is
stationary or moving at low speed until this
pressure exceeds the water pressure below the
ship and then escapes abruptly, resulting in
intense vibrations.
Permitted exhaust back pressure
The exhaust backpressure must be measured
during commissioning.
Measuring points of the exhaust back pressure (
À
or alternatively Á , M14x1.5) can be found on the
underside of the exhaust manifold at the engine.
It is the static pressure which is measured, i.e. the
measurement connection must be internally sealed
with the pipe wall. Measurements of the dynamic
pressure lead to incorrect results.
Permissible exhaust backpressure at full load and
rated rpm:
20−80 mbar
Caution:
Exceeding the permissible value leads to
an impermissible exhaust temperature and
to thermal loading, as well as to
inadequate engine power and considerable
smoke development.
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