I fill my 100 gallon horse stock tanks on a regular basis during the summer. I have a very good well with plenty of water and up until this last year I have had no problems. I was able to fill at least 2 stock tanks and sometimes 3 and still have water. In the last year, I have had problems where it seems like the well pump just loses it's prime and I have no water. I know it is not a problem with the amount of water because I restart the well pump within a few minutes and it pulls water immediately. I thought maybe this is a problem with the pressure tank so I checked the pressure and it is 45 psi. I have a 40 - 60 range on the well pump cut-in/cut-out. Any ideas on what my problem might be ?

Just to be sure things are clear, you are suggesting your pump is losing prime, so I am making the assumption the pump is above ground... correct? The pump is running, but there is no water coming out, but later you have water. If that is the case, then you are not likely to be losing prime. Once you lose prime, you have to reprime the pump to be back in business. It is possible you are pumping more water than your well can supply. Once it quits for a few minutes, the well refills enough to pump again for a while.

The tank is not your problem.

When you say you "restart" the pump, do you mean it has turned off and you have to reset the breaker? How do you restart it?

As stated your bladder tank isn't the problem. However, the tank PSI should be set at 38 PSI when the pump's shut off and the pressure bled down by opening a cold water faucet.
Is sounds like you have a faulty foot/check valve that's causing you to lose prime. Check it out and replace if necessary. Good luck, Tom

As far as losing prime, that was an assumption on my part. The pump is not above ground, it is in the well. When I run out of water, I am at the barn so I can't tell if the pump is still running. When I get back down to the house, the pump is not running and I restart the pump by pulling the lever on the pressure switch until the pump starts again and it always comes up to pressure. Something I did not mention earlier, if I only open the faucet at the barn to half on, which reduces the flow, I can fill the tanks as I did before with no problems. It's only when I open the faucet to full flow does this problem occur. So, does that mean that when at full flow, I am pumping more water than the well can handle ? If that is the case, then sounds like my well reserve has decreased over the years. As far as a faulty foot valve goes, is there anyway to verify that without pulling the pump ?

You have a submergible pump. No foot or check valve. Your pump will always stay primed as long as it's under water. I think you've put your finger on the problem,
sounds like my well reserve has decreased over the years It sure sounds like the water table has fallen and when the pumps runs out of water you pump air until it replenishes itself. You're not going to like the solution. Either dig the well deeper or if you have room lower the pump. Good luck, Tom