My feedback on main drains in an above ground pool...

[mas985]

Up close this is true, how about at a distance?

From my observations, it is true at a distance as well. The currents are stronger in the middle of the stream with the smaller orifice but off to the sides, the larger orifice has more flow. But I would expect this behavior since the more force you have in a particular direction, the further the flow should travel. You can actually prove this to yourself with a hose and an adjustable nozzle. The smaller the nozzle the further the water travels both above water level and below water level just to different extents due to the differences in density of air and water.

[Anonymous [GDPR] European in the UK]

Thanks Mark, something to pay a bit more attention to with the dye in the water. I did have some flow figures somewhere and there was also a slight reduction in the flow with the smaller orifice but that due to only a tiny amount of energy being used at the pump, icing on the cake really but good to examine.

By way of comparison, the other larger pool I mentioned runs at 125 watts, 1400 RPM moving 63 US GPM, 0.5 PSI on tank gauge. When needed ( to pass regulation) we can crank that to 100 US GPM, 464 watts 2150 RPM, gauge reading 2.7 PSI but the pump could do more, sadly the builders fitted 3 skimmers but on to one pipe so the max we can draw is 100 GPM. That is a standard setup but the M/D is plumbed on a 3 port to do inlet and outlet for heating or cleaning if required.