kitchen-sink
This pipe under my kitchen sink has a big crack in the area circled in yellow. (It's on the back side so it isn't visible in the photo.) Can I simply unscrew the nut at the top that I circled in red to replace the pipe? I'm afraid to just go ahead and try in the fear that I will put my kitchen sink out of commission. I'm already ok with disconnecting the hand-tightened nut at the bottom.
Update:
Success! I replaced the tailpiece with no problem. Thanks to all for the help.
Since the pressure drops for both hot and cold at this fixture, the problem is inside the fixture as you've already guessed. The first place to look is any aerator or filter screen on the fixture, debris gathering there will quickly slow the entire flow. Looking at the diagrams for your faucet, I believe that will be part P (the flow straightener) in this picture (Q appears to be a tool for opening the end of the spray assembly).
You can also verify the pressure from before the fixture is strong by disconnecting the hot and cold supply and running them into a bucket or drain to check the pressure coming from after the shutoff valves.
The problem could also be in the mixing valve and you'd need to remove and inspect the cartridge if it's there. basically anywhere after the two water lines merge could have a blockage.
I use razorblade 27 abrasive cutting disks on a 4" grinder . razorblade is a brand that holds up well but there are others very thin metal cutting blades that will do the job in minutes, yes on sparks but I have never started a fire and have cut every kind of metal with this method. I just measured a disk and they are 0.075" thick.
Best Answer
Yes - that's a "tailpiece" - the new one may be too long, if so, they are made that way so you can cut them to fit - but there's also considerable space to slide them built into the connections, so don't overdo cutting them down.