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I have a Sears captive air water tank (model No. 390.29171) that stores water pumped from the well. When we took possession of the house, there was no water in the tank or lines, the water pressure gauge was stuck at 95 psi (on at tank with a maximum working pressure of 75 psi), and the air pressure in the tank measures less than 10 psi.

According to the information on the tank label, the pre-charge air pressure should be the same as the cut-in pressure setting of the pump pressure switch.

My question is, how do I find the cut-in pressure setting of the pump pressure switch? If I remove the covers from the two pressure switch boxes, is there something that will tell me what the setting is?

The photo shows the pump cut-off pressure switch.  There is an identical box without a label to the left of it which is partially visible in this photo.  I'm guessing this is the pump cut-in pressure switch?

The photo shows the pump cut-off pressure switch. There is an identical box without a label to the left of it which is partially visible in this photo. I'm guessing this is the pump cut-in pressure switch?

Thanks in advance for any help.

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Pressure Switch

I've never seen a "safety cut-off" on a pressure system before, but typically the switching is done by a single box (known as a "pressure switch"). Pretty much all of them (at least from the last ~20 years) look something like this:

Typical pressure switch

The large nut is used to control the pressure (both cut-in, and cut-out) and the small one controls the range between the two.

Finding on and off pressure

First of all, you need a working pressure gauge to be able to do anything, so replace that.

To find the current setpoints:

  • Run the pump until it shuts off (this is the off pressure)
  • Open a tap or two, and wait until the pump cuts in (this is the on pressure)

Btw, 95psi is really high. Most homes run 40/60 or 50/70. International Residental Code maximum is 80psi (IRC P2903.3.1). Beyond that, you'll potentially start having issues with leaking toilet valves in particular, but other failures are possible as well.

Bladder tank pre-charge

Normally the pre-charge should be set to 2psi below the on pressure, but if your tank recommends setting it the same it shouldn't make a huge difference.

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