Pressure Tank Installation Using Pitless & Tank Cross
In this diagram, you will see a few essential components and the proper order they should be installed in. In this depiction, the tank is in the pump house, but the well is outside the well house. In that case, the water comes out the top of the well and then would hook back down through a union into the ground to make the trip over to the pump house or equipment closet. If the pump needs pulling, you will disconnect there at that union on the well head. The other way, would be to use a pitless adapter to exit the water well below the freeze line. The only thing that would come out the top of the well would be the pump wiring (through a vented well cap). If you don't use the pitless adapter setup, you can wrap this well head and piping with batt insulation (like you use in the walls of a house) and then drop a Dekorra Rock over it to weatherproof it. Bury the rock bottom edge in a 2" deep trench to keep wind out.
Next, there in the pump house, you'll want to install a backup check valve in case the one on the pump ever fails. This could save you a lot of grief (a pump, or even a ruined water well). In this drawinig, we show a simple #80 Flomatic check valve. If you use a tank cross, it will be next. This cross can have a union built right onto it making your next tank change out very easy. This cross is where you can install your pressure switch, pressure gauge, a pop-off, and a faucet. The pressure switch should not be further away from the tank than 5 foot so this makes that be fairly certain. Having a faucet installed in the tank cross allows you a place to get water out of the system even though you had to turn the water off to the house or garden for some reason. For example, you could draw a 5 gallon bucket of water here and use it to flush a toilet. Next, you will install the cutoff valve that would cut the water off to the house. Lastly, if you use a water filter, it would go in the line here as the last thing you install. As a water filter clogs up, it is like a valve closing, you would not want to put this filter anywhere else. When the on/off valve is closed, you can change out the filter element in this filter.
Note: If you have a pop-off valve on your water heater in the house, that could take care of a stuck or blocked pressure switch situation where the pump could pressure up way past the working pressure of the tank (a bomb). But otherwise, you might want to install a pop-off valve there in the tank cross you installed.
To set the air in your pressure tank correctly, note the "on" pressure of your pressure switch and with the pump off, no pressure in the system or on the lines, set the air in the bladder 2 lbs. less than that "on" pressure of the switch.
Example: 30-50 pressure switch = 28# in the bladder or diaphram, 40-60 = 38#