I have repaired copper pipes before but the way this looks gives me a little pause. The water flows from the source at the bottom left into the RPX and Backflow Preventer. When the valve is open using white handle at the bottom left it sprays from the two fitting circled. I was just going to cut out behind the fittings (now that I look at it I am wondering if those was repair fittings to begin with) and soldering in a new piece with repair fittings.

Am I missing something here, I wasnt sure what the fitting were on this pieces and was concerned they were part of the pressure reduction process.

[img][[/img]

I slept in a Holiday Inn.

I think those different sections of pipe do 2 things:
1) transition to a bigger size pipe, and
2) allow a bend to line up with the top piece.

I vote you are over thinking fixing it.

Those are pro press fittings and may have been used to repair but if relatively recent construction may be original. They basically have an o-ring inside a crush sleeve to seal. It looks like the diagonal piece is not aligned and maybe not long enough. They need to be square to the adjacent fittings. Can't see all in this picture but in this case may be that the valve moves with the ground it exits from and the threaded pipe on the outlet does not move or or moves independently. Since these have o-rings they can't be soldered and the ball valve is pro-press also so it would have to be replaced to solder. There maybe enough pipe to cut the 45 on the valve output and press on a pex adapter and connect rest with pex but you will want it covered.
Pro-press has applications but this may not be one of them.
This is just used to convey water not part of any pressure control.