I have a 1930s-era house with generally galvanized plumbing. The water-in line is a straight vertical pipe, except for this section which is perpendicular (and copper). The loop part is marked "Ford", the water comes up, to the right, circles around, then continues up. This looks like some sort of old-style expansion joint to me.
As you can see in that image, and this closer one, the right hand threading is leaking just a little, roughly a cup of water over 3 days.
Adding to the complications is that a few feet below this loop is the main water shut off for the house: an old gate valve that no longer fully shuts off the water, though it does shrink it to a manageable trickle.
I'd like to eliminate the leak before the basement is mildewed, but can't stop the water flow easily. Ideally, is there a way to install a new ball valve in place of this center pipe part so I can both deal with the leak, and have a reliable way to turn off the water? If not, is there a reliable way to replace that center pipe that won't leak?
(This sounds like a job for some sort of PEX, so I should admit that I've never used it, and have always been slightly distrusting of it.)