Raw Water Impellers

[km1125]

Source of the post Do you agree that the most water that could be moved by one rotation is the volume of water in between the vanes?

I would agree that would be the most theoretically possible, but none of that water actually gets pumped if you remove the cam. The cam gives you displacement. There is an ideal number of vanes, and that is the number that matches with the cam.

Think about it this way: If each vane - when compressed - displaced 1cc, then 10 vanes per revolution would displace 10 cc per revolution. 20 vanes would displace 20 cc. If you only had 4 vanes there would be a LOT of water held in the pump, but since each only displaces 1 cc, then there would only be 4cc pumped per revolution...the rest just goes in a circle for the ride around the shaft.

There is an upper limit though, which I'm sure is factored into the engineering. Too many vanes would not allow the full 1cc to be displaced. As Viper notes, the vanes also impact pressure. Pressure and flow are directly related, as when there is ANY resistance, higher pressure is needed to get flow. It's not as simple as "less area taken up by the blades means more water moved. "

[g36]

Source of the post g36-so what shape would you say the impellers are in after 2 years and how many hours are on them. .

sorry didnt see your post. on the river where i live we avg around 60 hrs /yr. there hasnt been issues with any blades breaking off and in general there still in ok shape maybe a few cracks here and there . i can service these on my 405 very easily so i have just set this up to do every couple years. i do carry spares you never know.
btw. i have, which works well for me, lowrance hds electronics and have used their nmea 2000 temperature sensors (i'm sure anybodys nmea 2000 would be the same) and have attached them to my exhaust and set alarms points so i can monitor and view the actual temperatures of the exhaust so if i have any issue with water flow i will know it right away.

[Viper]

Source of the post......temperature sensors.....attached them to my exhaust...so if i have any issue with water flow i will know it right away.

They're the best thing to have in temp monitoring IMO. People rely too much on their engine temp gauges to give them a quick enough response to a water flow problem so you can act before damage is done. I don't think most realize that by the time your gauge reflects you have a cooling problem, your exhaust is likely already damaged. When water flow to the exhaust is drastically reduced or stops as a result of pump failure, exhaust hose temps rise immediately. It doesn't take long at all for damage to occur. It's a "wet" exhaust system and the hoses are not designed to handle dry exhaust temps. Monitoring the temps at the exhaust provides a much faster indication of a cooling problem. It's a simply system, and easy to install.

[g36]

Yes I totally agree ! A great early warning indicator.