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Is my well pressure tank permanently waterlogged, do you think?

I have a private well that's about 100 ft deep. I have an old WellMate WM-25WB pressure tank. It's fed by an old Myers ¾ HP submersible pump. The property is new-to-me. I noticed what I think is the pump short cycling. In between a start and stop of the pump I get about 4 gal. I think this is considerably less than the drawdown capability of this 86 gal tank and the pressure switch settings.

I listened for the pressure switch clicks and then read the gage - 39.5 psi start, 57.5 psi stop.

Here's what I did: -No water came out of the schrader valve. -Emptied tank to 0 psi through the iSpring filter (sits about 2.5 ft above bottom of tank). Still has water in the tank as felt by gently rocking the tank. -Added more air to the tank, to get 38 psi. -Continued to pump out water via iSpring. -Got down to about 10-15 psi in the tank and the water turned very dark rusty. (This area is known for high Fe and Mn in the groundwater at 100 ft.) And then the water stopped flowing. -Tank rocked easily. -Added air to get 37.5 psi at the tank. -Flushed and flushed to get rid of the rusty water. I assume just the dregs of the tank. -After all diagnostics and flushing, a pump cycle yielded about 16 gal (a big increase).

What do you think? Any additional diagnostics I can do? Thanks. John

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  • When you replace it, put a drain valve at the low point, where one belongs. The set-up you describe (drain point 2.5 feet above the bottom of the tank) is "poorly done" at best.
    – Ecnerwal
    Commented Jul 30, 2021 at 12:10
  • Yes, definitely. I'll use a standard tank tee with boiler drain, pressure gage, pressure switch, and pressure relief valve.
    – coderjohn
    Commented Jul 30, 2021 at 16:42

3 Answers 3

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Start shopping for a new tank - your diagnostics indicate that you almost certainly have a failed bladder on a 20+ year old tank.

You can continue to add air as needed until you get the new tank, but it's tedious to do so. There's not much need to do the full drain and pre-charge when the tank won't hold the pre-charge pressure.

You may eventually have a more drastic failure if the tank corrodes enough, so it's good to take the time to shop carefully when the failure mode is non-critical, rather than having to pay "Whatever it costs to fix it NOW" when a more drastic failure is spewing water.

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  • Thank you. How often might I expect to need to add air for the precharge? How can I determine how many psi to add (without having to do the complete drain of the tank)? In my favor is that the tank is a WellMate fiberglass tank and I believe it has a "plastic" fitting for the outlet (hopefully minimizing any corrosion concerns).
    – coderjohn
    Commented Jul 30, 2021 at 16:47
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The old style pressure tanks without a bladder had to re-pressurized with air every few weeks as the new water absorbed the air in the tank. It was my job as a kid to re-pressurize/re-air the tank every few weeks on our family farm.

Newer pressure tanks have a bladder that prevents absorption of the air into newly pumped in water. But those bladders can fail. I have had one fail on me. You can then either keep "pumping it up with air" or replace the tank. There is no repair available, only replacement, or deal with constant need to pump air into the tank.

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  • Thanks George. I found a postcard in the info pack attached to the tank. It suggests that the tank is from the late 1990s. The current WellMate WM-25WB description says the tank is a bladder type. Could mine be of the type you describe "air over water"? When you say keep pumping it up, if it is the bladder type, do I have to drain it completely out, each refill time, before bringing it back to the desired precharge pressure?
    – coderjohn
    Commented Jul 30, 2021 at 3:01
  • No, this isn't an exact science (although others could disagree), If you notice the pump short cycling it means you don't have enough air in the pressure tank, it's that simple. In older, non-bladder tanks you just turn off the pump, drain out some water (again, not scientific) and add compressed air until it comes up to your normal pressure. If you over-do it, you'll be running some air out your plumbing, but it's OK, it'll equalize soon. That same principle applies to a tank with a broken bladder, they behave the same way.
    – George Anderson
    Commented Jul 30, 2021 at 6:09
  • ....continuing....not sure what you mean by "air over water", clearly water is heavier than air so the air cushion (which provides the pressure) would be over the water in a bladder type tank or non-bladder type. Re-reading your OP I think you did all the right things and made it a lot better. I does sound like your tank is approaching the end of it's useful life and you should plan for replacement within a year or two. If the bladder failed, you'll have to repeat the process you did every once in a while when you notice the pump is short cycling.
    – George Anderson
    Commented Jul 30, 2021 at 6:15
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I am assuming this ran for a long time. You did ok and yes it was waterlogged. If you replace the tank a bladder type of tank will keep you happy for a long time. Mine were still good twenty years later, I sold the home but they never had any problems. Important be sure there is no valve between the tank and the pump, closing that will probably blow the line in the well. My father fitted a tire valve stem on his tank and every so often he just added air using a tire pump.

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