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.