I should start by saying that I am the owner of a very old house. I am only 27, but don't let that fool you, I can do my own plumbing an electrical work, and can usually figure out any problem. When I moved in 4 years ago there was a jet pump and pressure tank in place in the basement. The jet pump was soon after replaced with a piston pump (free from family) which worked great for years and kept nice high pressure. The piston pump started failing, this morning it would only rise to approx 40psi and keep pumping, but without the pressure rising or the pump shutting off.

My father gave me a good jet pump he had laying around, barely used. I plumbed it up tonight, hooked up the old pressure tank, and flicked the switch. After fixing any leaks the pump runs fine, but once again only rises to 40psi, where it hovers and continues to run without shutting off.

I know the pump must be getting an adequate supply of water, because if I drain the pipes until the pressure goes down (to approx 20psi) and turn the pump back on, it rises to 40psi quickly.

I was wondering if maybe the bladder in my pressure tank could have lost most of its pressure over time? I know water won't compress, so I'm guessing maybe I only have a tiny amount of air in that tank, which maybe can't compress enough to give the 60-70 psi that the tank should reach. I worked on this until 11:30 tonight, I've given up and will tackle it tomorrow afternoon, but would like some fresh ideas. Looks like a brand new pressure switch on the pump, so that can't be the issue. Also the supply pipe going into my well is several feet from the bottom, so I doubt it's clogged or gunked up. I don't think the supply pipe is cracked on it's way up to the house either, there is a section just before the pump which is clear, and I see no air bubbles traveling through (as you'd expect to see, like sucking water through a cracked straw). Some fresh ideas would be great, I could use the help.