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cooled section of the exhaust line because of the ease of installation
and flexibility.
Provide adequate support for the rubber hose to pre-
vent sagging, bending and formation of water pockets.
The exhaust
line must be at least as large an I.D.
as the O.D. of the exhaust
elbow hose
attachment
nipple.
It should be
increased
in size by
1/2" I.D. for every 10 feet beyond the first 10 feet.
Always
arrange
the
rubber
hose
section
so
that
water
cannot
possibly flow back into the engine.
Also make sure that entering sea
water cannot spray directly against the inside of the exhaust piping.
Otherwise, excessive erosion will occur.
The use of brass or copper
is not acceptable for wet exhaust systems, as the combination of salt
water and diesel exhaust gasses will cause rapid deterioration of this
material.
MEASURING EXHAUST GAS BACK PRESSURE
Back
pressure
must
be
measured
on
a
straight
section of
the
exhaust line and as near as possible to the engine exhaust manifold.
The
engine
should
be
run
at
maximum
load
during
the
measurement
period.
Set-up should be as shown below.
1.
For normally aspirated engines:
Pressure Test
Mercury Test
1-1/2" Max PSI
3" Mercury
2.
For turbo-charged engines:
Pressure Test
Mercury Test
0.75 Max PSI
1-1/2" Mercury
Checking The Back Pressure
1.
Exhaust elbow
2.
Exhaust line
3.
Transparent plastic hose, part-
ly filled with water.
Measurement "A" may not exceed 39"
for normally aspirated engines and
19.5" for turbo-charged engines.
WATER CONNECTIONS
Water Column
=
39"
Water Column
=
19-1/2"
Exhaust
Elbow
Seacocks and strainers should be of the full flow type at least
one size greater than the inlet thread of the sea water pump.
The
str ainer should be of the type which may be wi thdr awn for cleaning
while the vessel is at sea.
Mount the strainer below the water line
to insure self-priming.
Water lines can be copper tubing or wire-wound, reinforced rubber
hose.
In any case,
use a
section of flexible hose that will not
collapse under suction, between the hull inlet and engine and between
the outlet and the exhaust system.
This takes up vibration and per-
8
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