I purchased house in February 2017 inspector approved well. One week after closing well stopped producing water. I installed new deep well Gould DW jet pump cannot get pressure up. Water comes up then pressure goes down stays at 20.
I am not sure, but I think that you are saying that the water comes out of the ground, and the pressure never gets above about 20 PSI... or you are saying that eventually the pressure rises to 40, but drops upon use to 20 pretty quickly, and the pump cannot deliver water even at 3 gpm continuously above 29 PSI.
Plumbers think they need to pull hoses up to inspect foot. I think the problem is the holding tank. I purchased new holding tank they have not changed out old to new, just want to pull lines. Should we change out the tank before pulling lines, or pull? Well is in basement difficult job and expensive.
This problem is not the pressure tank. The pump should be able to keep up with your kitchen sink faucet.
Tell us about your well. How large diameter. How deep? Since this is a deep well pump, you will have 2 pipes to the well from the pump. Your injector down the hole may be clogged. That seems most probable. I am not a pro.
If your casing is big enough, a submersible pump will work with a lot less drama. But if there was enough room for a submersible, I would have thought they would have put a submersible in. They are a lot better. It takes a 3 inch PVC casing or better for a submersible.
Also, is your casing in a pit, or indoors, or what?
Here are a couple of threads you might look at. You will tell us what fixes things in your case, please.
https://terrylove.com/forums/index.php?threads/low-pressure-low-flow-deep-well-jet-pump.52193/
https://terrylove.com/forums/index.php?threads/new-pump-not-building-pressure.61645/
