Quote Originally Posted by mas985 View Post
Yes, the total energy is less for a smaller orifice but the energy per unit area is higher directly in front so it is more focused and tends to push the water farther than the larger orifice. Same reason smaller spa jets feel more powerful.
Up close this is true, how about at a distance? The less overall power dissipates easier, the path decays. Because it's closer to the surface or pointing to the surface would help. It's like laminar flow jets all the rage but they are better than a conventional nozzle as that spray breaks up into the air because it's too turbulent to stay together. Just my observation.



Quote Originally Posted by mas985 View Post
Not quite. The 0.5 PSI is at 70 GPM (full speed). Pressure loss is proportional to GPM^2. Given your RPM and wattage, I suspect your flow rates are much much lower. For 10 GPM the PSI loss is only 0.01 PSI.
Yes true, my flow rate being around 31 US GPM would still be around 0.2 PSI (lazy guess, off to work) although my taper machined eyeballs probably less than the blunt end with smaller hole common to pool manufacturers.



Quote Originally Posted by mas985 View Post
First, cavitation only occurs in the impeller inlet. As water travels outward in the impeller pressure rises and the vapor bubbles burst. So all the damage occurs in the impeller and fairly close to the inlet. The volute has the highest pressure in the system so water could not boil there. But the reason most pools do not have caviation problems is because PBs tend to install plumbing systems that have much higher head loss in the return plumbing than in the suction plumbing and this keeps the pump from cavitating.
Yes, I wrote that badly, I meant the boiling temperature can be felt on the volute it's cavitation on the back of the impeller blades I was meaning, you put that so much better than me. I had to watch a YouTube video to re think what I had written. It was interesting to see the cavitation start so far ahead of the pump caused by the pressure drop in the valve the throttled down. https://www.youtube.com/watch?v=eMDAw0TXvUo
Because I have the pumps below the water line I don't need a self priming pump so the impeller design is different to a conventional pool pump even when the owners have the pump below water level they still use the "pool pump" cos that's what the label says......

Even running flat out at 2850 RPM I do not get cavitation, maybe because the pump increases rpm slowly it doesn't trigger the sudden pressure drop but also of course the dynamic head increases in proportion to the amount of water being moved
The massive savings in electricity, and less cleaning work with improved water clarity speak for themselves, Ben set out the Best guess idea and changed a lot of things, this is the first forum I have gone anywhere near explaining what I have done on pools but there would be a lot of very happy pool owners if they had the same system, running pools on a light bulbs worth of electricity! It's good for the co2 footprint as well, saving around 2 tons of co2 per season compared to a 3/4 HP motor and 1.5 HP probably double that.