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then water flooded the exhaust system every time the engine was shut off.

Water lift muffler.

then it fills the water lift muffler, the exhaust hose back to the engine, the
engine exhust manifold, then any cylinder with an open exhaust valve.



RB

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The waterpump used to circulate the cooling seawater through an engine, or the
engine's heat exchanger, normally has 6 rubber vanes on its impellor. As they
pass over a cam the water chamber gets compressed and the water is pushed
onward. If the vane get worn down, efficiency is reduced, but its also possible
for the vane to break off completely and either get ejected of lodged in the
cooling system. If a vane is missing, the pump might not seal when it stops, so
they could be a path for water to flow freely. The output of the water (in a
wet exhaust system) is the exhaust pipe just after the exhaust manifold - thus
the possibility of the water flowing back into the engine through the exhaust
valves.

Since on many, if not most, installations the injection point is near the water
line, siphoning is possible, thus the hose should have a high loop and a siphon
break.


"Scout" wrote in message
...
Jeff,
I've no stake in this thread but I am curious. The pumps I've worked with
(granted they are not for marine use) don't provide much backflow prevention
when not operating. The rotary vane pumps (we used them for moving gasoline)
depend on centrifugal force (and sometimes small springs) to maintain a
reduced clearance with the housing (and also allow for some wearing of the
vanes). What is the nature of the pump to which you refer?
Scout

"Jeff Morris" wrote in message
...
Why? The siphon break includes a loop that is about a foot above the
water.
Do you know what a siphon break is? It would appear not.

Actually, the waterpump impellor normally seals the path, but if a vane
were to
break off and go unnoticed, there could be a direct path - hence the need
for a
loop and "vacuum valve," commonly called a siphon break.


"JAXAshby" wrote in message
...
then the exhuast system floods when the engine is shut off if the intake
is
left open.

... if the exhaust
manifold ( at the water injection point) is below water at any angle
of
heel,

no ****, Sherlock. **That** is forbidden. And it only took you nine
days
to
figger it out.

It IS NOT forbidden. It is very common. The requirement is to have a
siphon
break. Wake up jaxie, the majority of sailboats are setup like this,
including
the boat in question. All your huffin' and puffin' doesn't change the
fact
that
you made a major blunder and now you're trying to save face.

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If the vane get worn down, efficiency is reduced

no, efficiency is NOT reduced due to wear (to say such means you don't
understand how the pump works). efficiency _is_ reduced due to a broken vane.

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The output of the water (in a
wet exhaust system) is the exhaust pipe just after the exhaust manifold

no, it is not. the water injection point is quite a bit after the enhaust
manifold in all low mounted engines. This is done to get the water injection
point well above the water line to avoid eventual troubles.

jeffies, don't confused the water injection systems you see on rod hot boats
(when you admire their dual or triple V-8 engines and silicone babes) with
their engines exposed in gas docks. Those engines are mounted well above the
waterline, so have not need to move the water injection point upward. It is
already more than high enough.

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Since on many, if not most, installations the injection point is near the
water
line,

that is a forbidden installation, not to mention dumb. If you find one,
correct it.

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"JAXAshby" wrote in message
...
The output of the water (in a
wet exhaust system) is the exhaust pipe just after the exhaust manifold

no, it is not. the water injection point is quite a bit after the enhaust
manifold in all low mounted engines.

Sailboats (and other low mounted engines) often has an elbow that raises the
exhaust several inches which then feeds into the injection loop. The net affect
is to raise the injection point several inches and provide a bit of protection.
However, the ABYC standards recommend a siphon break if the manifold is below
the water line, not just the injection point.

Here's the diagram of the new Yanmar 3YM30 with both versions of the exhaust.
Even the high version only raises the injection point a few inches. The exhaust
manifold is clearly less than a foot above the prop shaft, so a very long shaft
and an extreme down angle would be required to satisfy the ABYC requirement with
no siphon break.
http://www.yanmarmarine.com/downloads/drawings/3YM20%20(with%20KM2P-1).pdf


This is done to get the water injection
point well above the water line to avoid eventual troubles.

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Scout wrote:
Jeff,
I've no stake in this thread but I am curious. The pumps I've worked with
(granted they are not for marine use) don't provide much backflow prevention
when not operating. The rotary vane pumps (we used them for moving gasoline)
depend on centrifugal force (and sometimes small springs) to maintain a
reduced clearance with the housing (and also allow for some wearing of the
vanes). What is the nature of the pump to which you refer?

Smaller vane pumps are effectively positive displacement. The really big
ones like you're talking about aren't really PD. Also, most raw cooling
water pumps are described as vane pumps but the "vanes" are flexible
rubber molded with the hub, and instead of springing straight in and out
axially, they fold up as they rotate past the eccentric. This makes the
pump more effectively positive displacement, too.

That said, I wouldn't count on one to prevent backflow.

Fresh Breezes- Doug King

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Thanks Doug,
Yep, I know the style you describe. I assume they don't develop much in the
way of head, nor would they need to. Actually, it sounds like a fairly
cheap, albeit effective, pump. I also assume they are self priming, even
though they remain wet?
Walmart sells small "drill-motor" pumps with rubber vanes that are handy for
emergency pump outs. Cost about 10 bucks.
How long do these pumps last? One season? Two? On the other hand, I'm sure
most of the sailors here don't put many hours on their engines (LOL!).
Scout

"DSK" wrote in message
. ..
Scout wrote:
Jeff,
I've no stake in this thread but I am curious. The pumps I've worked
with
(granted they are not for marine use) don't provide much backflow
prevention
when not operating. The rotary vane pumps (we used them for moving
gasoline)
depend on centrifugal force (and sometimes small springs) to maintain a
reduced clearance with the housing (and also allow for some wearing of
the
vanes). What is the nature of the pump to which you refer?

Smaller vane pumps are effectively positive displacement. The really big
ones like you're talking about aren't really PD. Also, most raw cooling
water pumps are described as vane pumps but the "vanes" are flexible
rubber molded with the hub, and instead of springing straight in and out
axially, they fold up as they rotate past the eccentric. This makes the
pump more effectively positive displacement, too.

That said, I wouldn't count on one to prevent backflow.

Fresh Breezes- Doug King