If it's a bladder tank, use two pounds less than the cut in pressure.
Check the spec tag on your water tank. It should be 10 PSI lower than the factory settings. Normally around, 28 PSI for a 30 gallon tank. the air pressure is to be set at 2 to 3 psi lower than the pump turn on pressure.
The air pressure should be 2-3 psi LESS than the pressure switch cut on. If you have a good 30/50 switch, then 27-28 psi air is good. (this is measured when tank is almost empty of water.)Total pressure with this switch should never be more than about 58 psi
Check the pressure switch at the bottom of the tank by removing the gray cover and looking at the sticker on the underside. The right pressure is 2 lbs under the cut in pressure which is the lower of the two. For example, if the sticker says 30/50 then the right psi would be 28. If it says 40/60 then the right pressure would be 38. you need to first empty the tank completely of water before checking air pressure in the tank. then fill the tank to the right psi and then turn the water on to the tank.
House pressure, 75 PSI maximum.
Cut out pressure is between 115 and 130 psi... cut in pressure is no more than 25 psi below the cut out pressure.
The water pressure depends on the residual air pressure in the tank. Normally it should be between 30 -50-psi. Tank air pressure is important, it should be about 27-29 when water is nearly empty.
About 40-70 psi.
The size of tank is immaterial. ALL domestic well water pressure tanks should have 28 or 38 psi when nearly empty. The difference is whether it has a 30/50 or a 40/60 pressure switch on it.
A hot water heating systems water pressure should be 12-25 psi , the air in the expansion tank should be set around 10 psi but can only be accurately tested with no water pressure against it. Usually u can tell if the tank is bad when the relief valve on the boiler starts releasing water
up on the top of the tank there should be a air valve stem and most pressure tanks should have 30 to 40 psi bladder pressure but it all depends on your water pressure settings.
Generally the pressure in the tank air bladder should be 2 psi below the water pressure switch kick in (pump turn on) point. In this example of 48 to 68 Lbs the air bladder pressure should be 46 psi. This pressure should be measured with the tank empty of water, that is to say NO water pressure applied. NEVER over pressurize the air bladder - it would be better to under pressurize if in doubt. Some tank manufacturers may recommend a different PSI differential so check with the tank literature or the manufacturer.
You do this with the tank empty. First adjust the air from the nipple usually on top, to 28 psi, then switch on pump to fill tank. Now open 2-3 faucets and watch the gauge very carefully as pressure reduces. Adjust main spring on pressure switch to cut ON at 30-31 psi.