So I've been experimenting with the different speeds on the VSP. It looks like I can run around 800-1200 RPM with no solar, and 1800-2600 with solar on. The layout is simple with the filter output going to a 3-way valve for solar with the down pipe going out to the pool. Just below the 3-way is the solar return with a Jandy check valve.With the single speed motor there were no issues with persistent air bubbles. I realize that positive pressure has to be maintained at the top of the solar panels to prevent the vacuum relief from opening and the higher speeds take care of it. But the new problem is when running low RPMs with the solar off.
At low speeds my theory is that there is no water column in the down pipe to push the check valve closed. As a result of the negative pressure, air is getting into the plumbing from the empty solar panels via the vacuum relief. Only when I kick up the speed to over 2300 does the water column rise and the bubbling stop. Now when I looked at the Jandy valve instructions they recommend mounting the valve as low as possible in the system, so that means replumbing it to be near ground level. I think that would help matters, but not sure. The only other way I can think of is to replace the check valve with an automated valve working in tandem with the 3-way, meaning $$$. That would also prevent the solar from draining down properly. Any thoughts?