How come my shut off valves under the kitchen sink completely turn off the water?

Your descriptions are hard to follow yet understand! Is it the thread leaking or do you think part of the PVC has broken or is the spindle on the tap leaking? To fix either you are going to have to turn the main water supply off at any stage to repair any or all of those problems.!~ If a PVC cemented joint has come apart then you will still have to turn the water off & drain the system, co's PVC can't be re-glued while water is present, not even moisture!

If you don't turn the water off~~ Boy are you gonna get soaking wet in the process & then still, you won't be able to repair anything until you completely stem the flow of water! Unfortunately there's no short cuts when it comes to repairing water leaks! Cheers!

The water MUST be turned off and the line drained below the fitting before any action is taken. If these measures are not taken, you are wasting your time.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.