It's a long time since I used PDMS, but I'm guessing you want to "mirror" these valves in the model.
Gate valves and ball valves could probably be flipped, mirrored or whatever, as they are usually geometrically symetrical.
Control valves, check valves etc are not.
Flipping or mirroring these is not a PDMS limitation, but a physical one ..... you need to look at the valves to be installed, and see if these can be installed backwards, upside down etc, because this is effectivly is what you will be doing in the model.
Double check the valves from data sheets, cut sheets etc and find out exactly how it should be installed ... then figure out how to do it in PDMS.
Don't rely on the softwares limitations or controls for how you want to install piping items, just because the software allows you to do something, doesn't make it right or mean you should do it.
- If you're the smartest person in the room ... you're in the wrong room.