Can the plumbing parts curtain rod span 9 feet without a center suppor

Can be done IF you place the end brackets securely into the studs and the pipe and drapes are not heavy.

I would place a center bracket and open the drapes from the center to each side for a balanced appearance.

Use 1" or 1/14" electrical conduit. Comes in ten foot lengths.

If you don't have heavy curtains..........

I think it would be too heavy. What I do on my french doors, is use rods for each door. For a long window run, I have a support.

GENERALLY NO -- it will sag because of distance, and weight of the drapery fabrics etc. You can support from the wall at intervals, it's NOT rocket science-- do some planning . ALSO-- where your brackets- whatever you are using to connect to the WALL SURFACE-- paint the VISIIBLE UNDERSIDES to match the wall color. By doing so, you have the look of SUSPENDED ANIMATION! aS IN THE FLORIT BUSINESS- hide your work! I have light walls, with dark colored finished metal designer drapery rods-- looks as though they are just floating in space! I just re-read your post-- 9 feet long-- IF you use a continuous length METAL pipe of sufficient diameter, you could get away with it-- by SUSPENDING the ENDS from the ceiling- or just bracketing at each end--- the problem is the center rigidity and metal strength. USING PVC pipe IF thick enough may even work--- go to the big box stores plumbing departmets-- pull out a pice of 9' long pipe, lay on the floor to see if it's curved (warped) or has sag properties. It all depends on thickness of material and DIAMETER. Test it all first, THEN purchase what doesn't "bend!" AND ... make your own drapereries to fit the pipe work! GOOD LUCK!!! It IS DOOOO-ABLE!

I would most definitely use a center support...no matter the strength of the pipe. Gravity will always win.😉

I would definitely use a center support or the curtains will sag.