Expansion tank after filters/softener?

[nelsonr]

One of the reasons for an expansion tank in a closed system is to allow for expansion due to the water heater. With my current setup that works fine:
Well -> expansion tank -> well pressure sensor -> UV -> water heater

I'm planning on adding filters and a water softener after the pressure sensor:
Well -> expansion tank -> well pressure sensor -> 50 micron sediment (we sometimes have large particles I don't want in the softener or 5 micron filter) -> softener -> 5 micron sediment (prevent UV shadow) -> carbon block (prevent UV shadow from tannins + remove radon) -> UV -> water heater

Again assuming this is a closed system, as the water is heated couldn't that cause water to go backwards through the filters and softener to the expansion tank? Should this be concerning? If so, I assume I should be installing a backflow preventer after the filters/UV, which then would mean adding a second expansion tank right before the water heater:

Well -> expansion tank -> well pressure sensor -> 50 micron sediment -> softener -> 5 micron sediment -> carbon block -> UV -> backflow preventer -> expansion tank -> water heater

I haven't seen anyone recommend this so I assume it's not necessary? Thanks!

 

[Reach4]

Again assuming this is a closed system, as the water is heated couldn't that cause water to go backwards through the filters and softener to the expansion tank? Should this be concerning? If so, I assume I should be installing a backflow preventer after the filters/UV, which then would mean adding a second expansion tank right before the water heater:

Yes, water would very slowly go backwards. No, it should not be concerning. Yes, if you added a backflow preventer (check valve) you would need an expansion tank after the check valve, but don't think you will want such a check valve.

 

[Sponsor]

 

[nelsonr]

Yes, water would very slowly go backwards. No, it should not be concerning. Yes, if you added a backflow preventer (check valve) you would need an expansion tank after the check valve, but don't think you will want such a check valve.

Thanks for confirming. I couldn't think of any situation flow backwards would be blocked or would be a problem; even during softener regeneration it's open and you can use water.