Right, so what I've done yesterday is that I disconnected solar panels at a time to increase the pressure and remove any potential airlocks. I also ran the pump at full pressure for a bit to try and remove any additional air. I would say based on this that I shouldn't have any additional air to be honest.
Again, technically, this is not an airlock issue. Airlock prevents the flow of water but this is not what is happening. The issue is that there is not enough flow rate going to the panels because of the pump head curve and the head loss between the pump and panels.
Separately though, I've this morning also noticed that if I close my vac+sump+skimmer and open my topup which is coming from a well underlying the pool (perhaps 1.5m distance, flexible hose) the pressure immediately drops by a significant amount.
That means you are probably restricting the suction side and reducing flow rate even more. Ideally, you want all of those open. The more parallel paths for water, the lower the head loss and the the higher the flow rate from the pump.
With my solar open and inlets at 30%, I'm at 12psi only and with everything going to solar I'm at 14psi. As soon as I open any of the other 3 (vac/sump/skimmer) this increases by give or take 6 psi. Does this make sense?
Yes, perfect sense as I outlined above. When flow rate to solar increases, which is what you want, filter pressure will increase.
When all the suction side ports are 100% open and flow is only to solar, does air come out of the solar returns in the pool? What is the filter pressure in this scenario?
I was thinking that maybe the fittings are making such a difference, but I even tried removing the hose from my vac port entirely to just have it open and this made no difference at all ?! Since the pressure reduces so much with using just the topup valve, I ran this for a few minutes to make sure any air is pushed out... but as soon as I switch everything back it still doesn't make a difference to the pressure. I'm very confused as to why the vac/sump/skimmer make such a difference here really, and why would the topup not act the same? The only difference is that the well is further underground, but I don't see why that would effect it so much.
This goes back to explanations given above. The more the parallel paths, the lower the head loss and the higher the flow rate. This results in higher filter pressure. Also, fittings add head loss but each one is not that bad. Each 90 adds the equivalent of 4' of straight pipe and each 45 about half that.
But I still think there is something in your plumbing causing higher than normal head loss. If I calculate an operating point for your pump and plumbing setup, I get less filter pressure than you do even with a 28' lift. Do you have a link to the filter you are using or perhaps the manual? I want to see the head loss characteristics of the filter.
Not sure if this helps at all, but if not -
a) if I had to change the pump, is there something specific you would recommend by any chance?
b) if I had to instead consider a solar booster, I assume you are referring to a booster pump right? am I right in saying this should be placed just after the valve going to the solar panels? and again here, is there anything in particular you can recommend please?
Thanks again
Unfortunately, not knowing what is available in your country makes it difficult to make recommendations. But yes, a booster would go right before the water is sent to the solar panels.
But before recommending the pump characteristics, I would like get feedback on the test I outlined above (All suction 100% open, only solar return 100% open). Report filter pressure. The panels are back in the loop, correct?
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