Westerbeke 21A Manual de Instalação descarregar pdf (Página 19)

This leads to B, the amount by which the spill over point of

the exhaust outlet is above the worst case water level. B

should be maximized (and certainly always positive). Then

the exhaust loop height, C, from the high point spill over

point to the through hull fitting spillover point, becomes a

back up to B for preventing water intrusion, rather than being

the primary defense – as becomes the case whenever the

exhaust outlet spillover point dips beneath the water level.

But the height of C is also important. The only defense

against momentary passing waves, when they immerse the

exhaust outlet, is the exhaust loop height, C. If A has been

minimized, C will probably be in excess of a couple of feet.

The higher the better. Maximize this height, C, because it is

your only defense against a passing wave, rogue waves

included!

The verticality, D, of the hose run from the high point to the

exhaust outlet is also important. When a momentarily rising

water level immerses the exhaust outlet and is accompanied

by water velocity towards that through hull fitting, it is easier

for the intruding water to rise along a sloping hose towards

the high point than to rise vertically towards that high point.

Minimize D and keep this part of the exhaust hose as vertical

as possible.

Similarly, it is desirable that angle N be a 90 degree angle

with the exhaust hose rising vertically. This will further

discourage water intrusion, especially when backing down,

turning, or otherwise experiencing sea water velocity

towards the exhaust outlet.

E is the inside diameter of the exhaust hose. This should be

no less than F, the outside diameter of the generator’s water

injected exhaust elbow. E should only exceed F if exhaust

system back pressure requirements are not met.

NOTE: When the length of

is more than 20 ft, increase the

hose diameter

by 1/2 in to relieve back pressure.

G is the length of exhaust hose leading from the water lift

muffler to the high point. The shorter this length, the lower

the back pressure and the greater will be the reserve capacity

inside a given water lift muffler. The shorter the better, but it

is much more important to minimize A than to minimize G.

The water lift muffler should be sized to hold multiples of

the volume of water that spills back from the exhaust high

point when the engine/generator shuts off. The actual amount

of normal spill back at shut down is a function of length G,

the exhaust hose inside diameter,

, and the sea water pump

flow rate. The larger the muffler the better. Remember -

when all else fails and water comes pouring over the high

point, only reserve capacity in the muffler can contain it and

prevent it from entering the engine/generator.

H is the height of the engine’s water injected exhaust elbow

outlet above the top of the water lift muffler. This should be

maximized. This length of hose is additional reserve capacity

to contain both intruding water and splashing inside the water

lift muffler.

J is the total height engine exhaust gas pressure must move

water up hill – from the bottom of the muffler to the spillover

point at the exhaust run high point. J is driven by other

installation dimensions. It results from a conservative

installation, rather than being a driving factor. In most

installations, J would not exceed 4’ (1.2m), this height should

produce adequate exhaust system back pressure level.

EXHAUST SYSTEM INSTALLATION

▲ WARNING:

Use extreme care during installation

to ensure a tight exhaust system. Exhaust gases are

deadly.

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