I'm no physicist, but we run into cavitation when running the pumps on our fire engines. Basically, a pump creates a pressure differencial. When your pump creates a condition on the inlet side of the pump where the pressure is lower than the vapor pressure of the water it is pumping, then bubbles of water vapor are formed. These bubbles collapse when the water that they are in reaches a higher pressure- that is, when that water passes thrugh the pump to the outlet side. When you have a pump cavitating, you get a thumping sound like you have a cement mixer full of large rocks. It  can destroy an impeller in pretty short order. I think that the reason that a restriction on the outlet side of a pump might decrease cavitation is that the flow of water through the pump is restricted more than the the flow up to it, so that the pressure differential  on the inlet side cannot drop below the vapor pressure of the water. This does not seem to make sense, given that a typical cooling

system is supposed to be closed, and that water is practically incompressible, but
there is a little room for expansion, and that is what is required, a little room for
the volume of the cooling system to expand enough for vapor bubbles to form. This is
a simplification and it does not address all of the dynamics of a cooling system.

I know we haven't heard the last  of this string.

I will get the dimensions for the planetary gearset mentioned earlier. It appeared exactly the same size as the C-6 gearset to my uncalibrated eyeball.
Brian Trubee

 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org