Well X-Trol 119gal. Old.

Pressure switch set at 40-60.

At rest and without power to the pump after all water has drained from tank, pressure gauge reads 0.

Tank is reading 15lbs of pressure from my air gauge.

Turn pump on, fill tank, turn yard sprinklers on:

Bad Behavior: When pressure falls to 40, pump kicks on. Pressure builds slowly (normally) until about 47 then jumps to 60 immediately. Pump stops. Pressure drops immediately back to 47. Pressure drops slowly (normally) as water is being used until it hits 40 and the pump kicks back on.


Ideas on the status system?

(Edit: I know the tank should hold about 38lbs of air. I topped it off months ago, and the air has dropped to 15lbs)

  • Does the tank have an air bladder or just uses the air in the water tank itself to smooth out pressure?
    – crip659
    Commented Jul 15, 2023 at 14:01
  • Yes, it has a bladder.
    – Terrence
    Commented Jul 15, 2023 at 14:14
  • Possible the bladder or the air valve has a leak. Fill it up again and see.
    – crip659
    Commented Jul 15, 2023 at 14:30
  • Mr. Soapy bubble told the story. Replaced stem valve, pumped it up to 38 and is holding. Certainly should have done that before posting.
    – Terrence
    Commented Jul 15, 2023 at 16:13
  • This doesn't rule out a bad bladder though does it? I put on new (china) union joints at the T, 6 months ago, and they are showing signs of rusting. Doesn't rust indicate a bad bladder?
    – Terrence
    Commented Jul 15, 2023 at 16:15

1 Answer 1


With the obvious suggestion from @crip659, thank you, I topped off the tank with 38 lbs of air and the tank is cycling properly.

The rust mentioned in the comments is troubling.

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