Expansion tank Pressure setting

[Onokai]

I'm adding a small 2 gallon expansion tank to my 80 gallon solar water heater which feeds my 40 gallon gas water heater, I'm putting it in the incoming cold water line from well with a 40-60 pressure switch.
What air static pressure should the tank have in it charged before the install 38#s? of split the difference at 50#s?
Thanks
mark

 

[Reach4]

I was going to say 60, which would be the right answer if there was a check valve in the path.

If there is no check valve, I could see 40 or 50, which might minimize reverse flow through your softener.

I have no check valve and no expansion tank, so my 44 gallon pressure tank takes up the expansion. The main downside is that there is some phantom water use registered by the softener as a result.

So optimum would be 60, but add a check valve between the softener and the WH. I am undecided what to choose if you have no check valve.

 

[Sponsor]

 

[Valveman]

With no check valve between the WH and well pressure tank, you don't need an expansion tank.

 

[Onokai]

I put in a check valve as I have a spun calcite tank that gets the well water first and I want the back pressure off this tank so the one way valve is a few feet past this tank before expansion tank. The reason I'm adding this tank after 39 years is my solar water collectors on roof (for 39 years) can get pretty high pressure when overheating before the older style drain down valve kicks in. The system is pretty complex as this solar roof collectors loop into the 80 gallon tank as well as i recently added my own solar electric ground array and use some extra power to also heat a 3500 watt element in same 80 gallon solar tank as the hot water collectors feed into. I also have past the water heater the newer Grundfos smart hot water loop pump for instant hot water at all home taps. The solar loop pipe rattle a bit now and then so I thought the expansion tank will help this condition. The well is 140 feet away downhill.
I'll set that pressure at 60 psi-thanks for the replies