Right, but engine water is derived from suction pressure. If too much water blows past the wear ring that will drop suction pressure. I have to say I agree with Tom on this one.
Not 100% accurate, but really close, the cooling water actually comes from the centrifugal force/pressure of the impeller spinning around, and if the wear ring were worn/loose the backpressure would be "diddly squat" because the backpressure just gets pushed through the wear ring back to the inlet of the impeller.
Basically you are correct, the water does come from the "back side" of the impeller but not the "suction" side.
Broken down there are four different pressures on a Berkeley, Dominator, AT pump;
1.
Suction pressure, it is exactly what it sounds like, but if the boat travels fast enough and things are working really well this area (in the suction piece of the pump) this becomes positive.
Lowest
2.
Back pressure, again exactly what it sounds like, anytime something spins there is centrifugal forces that fly outward, this is after the inlet side of the impeller, but before the outlet. (see drawing).
Second lowest.
3.
Pre stator pressure, or impeller outlet pressure, this is what you would measure whats in the bowl before the stator.
Highest
4.
Pump outlet pressure this is the water pressure available to go to the nozzle and push the boat.
Second highest. (seems wrong, but is right)
Hope this answers more questions than it asks!
Spent a lot of time playing with pumps to better regulate the amount of water pressure used for cooling. You actually can really change the pressure and volume by changing the eliptical shape of the depression.
