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  1. #1
    JRINJAX's Avatar
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    Would like some "Black-Belt" Pump information on pump over-stuffing.

    Since I know very little about PWC pump design [even though I engineer pumps and Hydronic systems for a living] can some one explain to me PWC pump design and the intricacies of pump over-stuffing?
    I had a shaft seal go bad in my Honda and it did not leak at idle, but riding it with the seats off, I saw the seal spray under high pressure at certain speeds/RPM/Throttle settings. This means that the area in front of the pump inlet must be at high pressures under certain conditions [like WOT] to pressurize the shaft seal like it does.

    Please give me a Pump Overstuffing 101 course so I can understand the physics of it or point me to where someone posted one.
    Thanks Much!
    JR


  2. #2
    JRINJAX's Avatar
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    TTT anyone?

  3. #3
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    At idle the impeller is sucking water,espicaly when you nail it. Due to the limited size of the inlet for warter acess. Now you are going say 65 mph,things change as the pump has a lot of water now being forced in to the pump from forward speed. pressure starts building as the pump loses its abilaty to process and spit out all the water thats being forced in from speed. There is a point where the water cannot go out the pump and will reverse flow and come back out the intake. this lifts the rear of the ski and in most cases the boat will turn unexpecdly because it steers from the rear and the normal stering function (rudder action) of the hull is out of contact with the water.
    Hull drag and all kinds of factors have dramitic effects of this and in most cases a soope grate takes care of this by changing how the water enters the pump and also holds down due to scooping action of the grate. So its common to see pressure in the pump tunnel as speed goes up. This can be relived in other ways as well but expermetion is very dangerous. Lots of talk about this in the yahama forum.

  4. #4
    JRINJAX's Avatar
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    Thanks much, does the size of the pump inlet and it's length/ramp angle make a difference?
    I have glanced at the pump inlet on the faster 'skis an noticed a longer more narrow inlet with a shallow ramp angle. The Honda intake is wide and short which might supply more water during the launch but seems like a disaster at higher speeds.
    Is this correct?
    Thanks much,
    JR

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