So I understand about setting the blatter pressure to 2 psi lower the pump turn on pressure. But how full or empty should the tank be before setting the blatter pressure.
Should you turn off the pump run the pressure down to 0. Then set the blatter pressure to 38 psi..?

Thanks

Hi! targabill, welcome to AMHD :)

Courtesy of:
inspectapedia.com How much air to add when restoring lost air in a building water pressure tank - private pump and well system do-it-yourself repairs (http://www.inspectapedia.com/water/WaterTankAir4.htm) 'bout a third of the way down the page in the Don't put too much air into a captive-air bladder-type water tank: section.

In general, bladder type water tank manufacturers recommend that the tank be empty of water when you set the air pressure in the tank to the specified psi. If you set the air pressure to the specified psi while there is water in the tank, the air volume will be incorrect (too small) and the water tank will not perform properly.

If you want the cut-in at the switch to be 40psi, then yes the bladder pressure would be 38psi with the tank empty.

K

Thanks so much...

how full or empty should the tank be before setting the blatter pressure. The tank should be empty, the pump shut off and the pressure bled off before setting the bladder tank at 2 PSI below the cut in point of the control box. Good luck, Tom

Targ, the only problem I see with what was posted above is this: How can you tell that the tank is 100% empty? I guess you could undo the piping and drain it that way, but the reality is you drain the system down to zero and set the pressure. At that point there will be little to no water in the tank, but unless you have X-ray vision you won't know for sure. If you have a faucet lower than the level of the tank, that might make it possible to drain everything out. Frankly, I wouldn't worry about it.