I recently lost water pressure so I checked the pressure tank pressure. The pressure was only about 18psi. The pressure tank is an Amtrol product and has a bladder that was precharged by the MFGR at 38psi 17 years ago. Anyway, I wanted to get the pressure back to where it is supposed to be so I shut the pump off and immediately noticed for the first time that the water was backflowing to the well and the entire house was drained. I didn't know why that was happening but noticed that there was no backflow check valve that I can detect between the tank and the submersible pump. This made me presume that there must have been some sort of backflow diaphram that deteriorated, I'm not sure. A plumber told me that pressure tanks have no such thing built in and advised me to install one before the pressure tank so I planned to do this but still wanted to fix the pressure problem at hand so I filled the tank with a compressor by adding air to the valve on the top of the tank until it reached 38psi but first I inspected the valve to see if water or air would be discharged and found that only air. I was told that was a telltale of whether a tank bladder may have burst or not. Anyway, I then turned on the pump and the water lines and tank began to refill. When the filling was complete I noticed that the contacts to the pressure switch were still engaged so I shut the pump switch off to inspect and once again the water started backflowing to the well. I would like to know if anything stated would indicate that the pressure tank or pressure switch may be defective and why. Also, the plumber I spoke with suggested that maybe a backflow valve could have been attached to the submersible pump. Is that plausible? I can't figure why all of a sudden this backflow affect is occuring. I am thinking that since the water now wants to backflow that adequate pressure can't be maintained so the pump wants to continue to achieve the cutoff psi. Does this sound right? Thanks

The pressure switch is bad. If the switch was good and the system was siphoning, it would be going off when the high limit pressure was achieved, and back on when the low pressure limit was hit. Install a check valve before your pressure switch when you change the switch.

Submersible pumps come with a check valve on the outlet of the pump. I install another one just under the well cap down in the well. A check valve at the pressure tank is usually not a good idea. It prevents you from teeing into the water line outside, such as installing a yard hydrant , or feeding water to another structure.

Most people aren't going to install anything like that after the fact however..