On Thu, 25 Sep 2008 00:25:01 +0000, Larry wrote:

"Roger Long" wrote in
:

I forgot to answer Larry about the jets injesting stuff. The
impellers in these things are pretty industrial grade, think tree limb
chipper rather than jet ski plastic part. They will digest pretty
much anything that will fit through the intake grates and is low
enough in density to either float or be sucked up from the bottom.
The impellers may get chipped and lose efficiency but, unlike props,
they don't immediately start vibrating so badly that they have to be
pulled. You can keep operating a damaged impeller for quite a while.



None of the jetski pumps use plastic impellers or stators. The
impellers are stainless steel with very close tolerances between the
impeller and wear rings around them. The stators are cast aluminum and
objects won't cause them any harm passing through the pump, either.

However, the problem with Mercury Sport Jet and jetski pumps arises
because the distance between the aft end of the whirling impeller at
high RPM and the fixed stator vanes is only about 1/4". ANYTHING over
1/4" is SURE to get WEDGED between the impeller and stator. This will
rip the gearboxes right out of them before any kind of sheer pin breaks.
Sometimes the drive shafts, both vertical and horizontal simply break
apart from the kinetic energy of the impact.

I was just wondering how much flowline clearance between the impellers
and fixed parts like a stator there is in these big pumps to prevent
such catastrophies from occuring.....

Thanks for the answer, however.... Let us know how much trouble it is
to clear the long tubular weed stalks out of the pump are WHEN, not if,
it happens....(c; I sucked up a ski rope one time and the floating
handle was the ONLY part that wouldn't fit through the intake grate. It
ate the aft end shaft seal and sleeve bearing that normally runs in
thick oil, which was ejected by the water pressure when the seal was
simply smashed away. The noise of the outer edge of the impeller
crashing into the pump housing from the lack of a rear bearing tight
enough to prevent it was DEAFENING! So wasn't the silence for about the
first hour after the emergency shutdown.

The entire pump had to be disassembled, the impeller removed while
cutting off the wound rope so tight it locked the impeller threads solid
to the horizontal drive shaft. The rope actually MELTED UNDER WATER
from the frictional heating into a solid blob of polypropylene....no fun
at all that day.

We once sucked up a ski rope with our Turbocraft. It was no big deal.
We simply unbolted the U-joint and turned the pump backwards with a
pipe wrench [It has a tubular auto type shaft] while pulling on the
rope. No damage, and it only took about fifteen minutes to fix the
problem. It didnt go all the way in. I wasn't there, but apparently
the operator shut off the engine before matters took their course.

Casady