Pump stumped.

I had a 1/2 horse centrifugal pump/pressure tank combo. The pump started to short cycle. It is set at 25/45. I shut down the water pressure and checked the air charge - 4 psi. I pumped it up to 18 psi. It dropped again. Ruptured bladder. I replaced the tank with a larger(40 gal) horizontal pump. It was preset to 40 psi. I brought it down to 30 psi.
I did not disconnect the pump from the well; just connected the new tank. I did not prime the pump as it had always started up well and not having disconnected the pump it should not have any air. The pump winds up to 30 psi, stutters there(the gauge) and keeps running. I can open a tap and it will run all day. When I pull the plug, it holds at 30 psi. The foot valve is ok.
I got a new impeller kit and replaced it - same result. I shut off the valve immediately after the tank - same result.
I installed a 1/2" plug on top of the pump rig to check for air. It is primed. It sounds like it is churning but when I check there is no air in the impeller chamber. Why would a pump not be able to make 45 psi? Thanx for you consideration.

Either you have some junk in the impeller or the jet is plugged. 28 psi is usually all a jet pump will make with a plugged jet.

bob...

stumped

Thanx Bob. I suspected the same. That is why, as I say, I put in a new kit. There is no jet, at least like the 3-4" ones I have seen in the past but I will look again.

If you have just a centrifugal pump, they are not recommended for the usage you have. A jet pump would be better suited. If it is an end suction, a bubble of air will keep it from priming.

bob...

Pump stumped

I was wrong. The box says it is a jet pump. It does not have the snout that I remember on the old jet pumps. The old impeller/diffuser that we replaced did have junk in it and we did not check for jet blockage. Will do that now. Thanx again.

For the system to work properly, the bladder tank must be BELOW the turn-on pressure by about 2 pounds. If your 25-45 switch is adjusted properly, you should have 23 pounds in the tank with it unloaded (i.e., no water pressure.

You want to drain the tank empty of water. If you don't, the water left in it will displace air and the air volume won't be what it is supposed to be. Then the bladder will be stretched, that causes premature failure.

Also, unless you use a portable air tank that has been filled awhile ago so the air is room temp, you normally will use a compressor which will heat the air, So you should set the pressure closer to or at the cut-in pressure setting of the switch so when the air cools, the pressure will be 1-2 psi less than the cut-in setting.