I have a water well with two galvanized tanks... one larger (220 gals.) than the other (120 gals.). Both are hooked up together with incoming water filling into the smaller with a Tee connecting to the larger tank. Once all the connections were done, I started the pump and noticed that after awhile (at around 15-20psi) the pressure relief valve on the large tank started to eject water. I don't have a pressure relief valve on the small tank, but do have the pressure gauge on it. The larger tank doesn't have a gauge. Does anyone have any suggestions?
Thanks.

While the pressure valve was ejecting water did the smaller tank pressure continue to rise?

Is the pressure relief valve a new one or an old one, if it is old it could be stuck open and if that is so the 15 to 20 pounds of pressure is enough to push water into the large tank without raising the pressure very fast because of the pressure valve being open.

Does the pressure switch ever turn the pump off?

the pressure relief valve on the large tank started to eject water. I don't have a pressure relief valve on the small tank,
I fail to see the reason to have a PRV on either tank. The pressure's not going to raise any higher then the control box cut off point. For that matter I fail to see the need for two tanks at all. Am I missing something here? Tom