If I backwash at low speed, it seems to work fine. Certainly not getting as clean as it ought to, but the basic function seems to work. But when I run the backwash with the pump on high speed, it eventually runs dry. Sometimes nearly instantly, sometimes takes a minute or two, but eventually it overcomes the ability to draw water from the pool and must be getting air from somewhere. Where's the problem likely to be?
My first thought was an air leak. I was getting a fair amount of air in the pump basket over time on low speed, so I rebuilt the Fibropool (jandy-alike) shut off valve coming from the skimmer. Now it holds up much better, and only builds up a bubble of air very slowly, over the course of days it might get to a bubble a few inches across. That's the only place for a leak in the plumbing, it goes directly from the skimmer to the pump. So maybe it's drawing in air through the o-ring on the pump lid? But it's only on high speed that it becomes a problem, and it occurs very quickly, it'll be fine one second and empty three seconds later.
My first thought was an air leak. I was getting a fair amount of air in the pump basket over time on low speed, so I rebuilt the Fibropool (jandy-alike) shut off valve coming from the skimmer. Now it holds up much better, and only builds up a bubble of air very slowly, over the course of days it might get to a bubble a few inches across. That's the only place for a leak in the plumbing, it goes directly from the skimmer to the pump. So maybe it's drawing in air through the o-ring on the pump lid? But it's only on high speed that it becomes a problem, and it occurs very quickly, it'll be fine one second and empty three seconds later.
