GENERAL
The exhaust system must efficiently expel all engine
combustion products and muffle exhaust noises with
minimum back pressure. If back pressure is too high,
the volumetric efficiency of the engine is reduced,
fuel economy drops, exhaust temperature increases,
end valve life is shortened.
Back pressure must not exceed
27
inches
(686
mm)
of water column for the rated load when measured
with a manometerat
the
exhaust manifold, Figure
3.
FIGURE
3.
BACK PRESSURE TEST
WITH
MANOMETER
Exhaust
Smoke
A light gray or light blue smoke is a result of low
ambient temperature and light load. This smoke is
unburned fuel (not harmful to the engine) and
disappears when more load is applied.
Black smoke indicates overfueling (more fuel than
oxygen) and is usually caused by overloading. The
smoke or unburned fuel becomes carbon when raised
to a high temperature. Carbon contributes to engine
damage because it sticks to rings and fuel injection
nozzles.
EXHAUST GASES ARE DEADLY
-1
POISONOUS!
Vent exhaust gases outside. Use flexible tubing only
between the engine exhaust outlet and rigid piping.
WARN~NG
On service calls, always inspect exhaust
=
systems for possible leaks. Report any ex-
haust hazards to theowner/operatorand warn them
of
the potential
dangers to life
if
not repaired.
INSTALLATION
TIPS
Points to remember when installing an exhaust
system are:
Exhaust pipes should be as short as possible with
a minimum of fittings.
The muffler must be as close to the engine as
possible. Mufflers which are too far from the
manifold remain cool and collect carbon residue.
Pitch exhaust pipe upward from exhaust outlets
to avoid entrapment of rawdiesel fumes in muffler
at shutdown.
Avoid sharp bends by using large radius elbow.
Check back pressure with a mercury or water
column type manometer.
Position the exhaust outlet away from the engine
air intake.
Exhaust noise can be suppressed or reduced by:
Using a heavy duty exhaust system with a more
efficient muffler.
Avoiding use of flexible lines.
Installing a deflector at the exhaust outlet to
direct exhaust toward the ground, but away from
the operator.
Using a resonator in addition to a muffler.
The importance
of
exhaust systems (normally
supplied by the customer) cannot be over-
emphasized.
A
poor or clogged system causes low
power, overheating and engine damage.
A
poor
exhaust system increases back pressure which
reduces efficiency.
If
the manufacturer tailon his own exhaust
system, an Onan applications engineer must
approve the installation for warranty purposes.
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