Another expansion tank question

As I recently reported, I installed an expansion tank for my water heater. The illustration on the box it came in shows a check valve in the supply line before the expansion tank. Is this necessary/desirable and if so, would a simple flap check valve suffice?

I'm guessing here, but I don't think you need to add one, as there probably already is one which is the reason you needed the expansion tank anyways? If this was a pump/well situation, then yes (maybe, since there may be one in the pump plumbing already), in your case, no.

not necessary

usually thier is a check valve in the meter comming
into the house from the city water line....dont bother

we would never install a check valve into
the line to the exp tank.

their is another plumber in our town that has been installing a
ball valve in the line to the expansion tank......to isolate the
water in it , I guess.

I think or guess the only reason he is doing this is becasue
the tank holds a few gallons of water under pressure

So when you shut the water off to the hosue you still have a substantial
amount of water under pressure built up into that tank....
and it takes a minute or two for this all to discharge .....

possibly flooding out someone, I suppose.

I'm all for isolating the tank with a shutoff valve. It will make replacing it easier too, when it eventually fails.

OK! No need for the check valve. If/when the tank fails, I can just unscrew it from the line and put a cap on the tee in its place so no need to do a valve. Thanks again, guys.