two-speed with solar panels

[mas985]

If the highest point of your solar panel is 20 ft above the pump, you will need at least 9 PSI to get to the top of the panels, 2 PSI of friction loss and another 2 PSI or so to close the valve for a total of 13 PSI. By my estimates, you will have about 12 PSI after the dirty filter or 1 PSI at the top of the panel which may not be enough to close the valve. I suggest cleaning after 4 PSI rise instead of 6.

As for two speed, as long as the pressure does not drop below zero PSI when switching to low speed, the valve should stay closed. But this does require a proper prime at high speed so all of the air is purged from the system. If not, when the pump is switched to low speed, the valve may open.