Brand New Taco Backflow Preventer leaking through center port

you have a piece of dirt solder, teflon , something stuck inside

Water enters from the left side the pressure pushes an inner spool against a washer or o ring see the t shape cut away of an o ring? The end of the brass spool contacts that

This closes off the bottom port , If water drips right away, something is lodged in that seal.

They are fairly easy to disassemble and clean out

Should be a strainer on the inlet? That generally catches most any problems?

This is a Caleffi, but they are all similar inside

is that a Watts? Always willing to help, but I don’t have any experience with that Valve

hot Rod is brilliant!!