two pipe deep well jet pump

i am helping my friend work on his well system. He has a two pipe deep well jet pump with new poly pipe,ejector and foot valve. The tank and pump are in the well pit. The pump will run forever if the pressure setting is above 40psi and it stays at 40...what prevents the pressure from building up any higher? He has a goulds pump and a bladder type expansion tank both look like they are less than ten years old. The pressure in the tank is 18psi empty. i turned the pump on and the pressure goes up to 40. I adjusted the pressure switch to turn the pump off at 40. With the kitchen faucet running it takes about ten to fifteen minutes to drop the pressure to 20psi. BUT... the tank empties itself it seems because when the pressure gets to 20 it immediatly drops to nothing everytime and the pump comes on and goes through the same cycle... from 40 to 20 and quickly to zero and the pump comes on. could there be a blockage inbetween the pump and the tank tee? Is the tank bad? It would be nice to see a higher pressure and not have the pressure drop like that before it cycles back on. Also i dont know if this is helpful or not but i also emptied the tank and bumped the pressure to 28psi and noticed that the pressure went up to 40 and shut off but there was no water in the expansion tank. what would cause that to happen. Thanks for your time.

You don't say what settings teh pressure switch operates at; like 30/50 or 40/60 psi. And with no water in teh pressure tanks you need 1-2 psi less air pressure in the tank than the turn on the pump switch setting. I.E. 30/50 gets 29-28 psi air presure with no water in the tank.

Do that and see what happens. If the pressure gauge doesn't read 0 when the tank is drained, replace the gauge.

When you drain the tank, check the tubing to the switch from the wet end of the pump and the tubing fittings and the holes the fittings screw into for blockage.

If then the pump doesn't go high enough to shut itself off, then you may have a blockage of the jet or a water leak in the pressure line etc.. You did replace the jet and venturi with the right ones for your pump right?

The pressure switch was a 30/50 but never got to 50 and the tank pressure was 27 psi. I checked the 1/4 inch tubing and there was some stuff in the line. I cleared that and pulled the lines out of the well and the fittings were tight. We bought a deep well ejector and we swapped out the venturi tube to match what the paperwork said for a 60 foot pipe length. The pump is 3/4 horsepower. The ejector box said it was for a 3/4 hp deep well up to 100 feet. I lowered the tank pressure down to 18 psi and put a 20/40 switch on the pump. The water runs for a good bit and the pressure does not drop to zero psi before the pump comes back on anymore, so that's good! The house was empty for three years before my friend purchased the house, could the pump possibly be corroded from being dry for those years? The well pit is humid, a good atmosphere to cause rust. I was afraid to pull the pump housing apart to look at the impeller without having a new gasket on hand. Thanks for responding and giving us some things to look for.

You didn't need to buy and install a new switch to change the settings. All switches are adjustable; 20/40, 30/50, 40/60 etc..

There could be something with the impeller.

Great, Thank you for the help! I'll take a look at it.