inside the well pressure tank

Works good; Seems to me it was like $800. Yep, needs a different well head/pitless adaptor assembly.

Allan

(You can get a surplus 3HP VFD for less than the cost of a Franklin 3HP single phase pump controller.) For stock watering, set the VFD up for (say)a 5 second frequency ramp and you don't really need a pressure tank. Just flip a switch when you want water, turn it off when you are done. The slow ramp rate eliminates the start-up current surge so the pump does not need to run as long.

For extra credit, you can use a PID feedback loop for constant pressure at variable water loads, but this may be overkill for stock watering.

I did this for my home water well, because I wanted a 3HP pump but did not want the three large pressure tanks needed to go with it. Instead I use one modest size pressure tank. It has worked fine for 3 years so far.

On bored wells its not so uncommon to find tanks (and pumps) suspended inside the well, but a 6 inch drilled well? I doubt it.

Charles

I'm not crazy about being totally dependent on the pump, I'd rather have large tankage, that way you've got enough to flush the commode if you have a power outage, and wash your hands. With a variable speed, it sounds as if you are totally dependent on the pump and power at all times.

Charles