What do the cylindrical metal parts do in a Delta shower cartridge?
Faucet leaks, installed new seat springs and rubber piston like washers. Still leaks. Delta sends me a new cartridge for free. I start poking around with the old one trying to determine the failure mode.
Got the basic water flow figured out. Water enters rear and up front a rotating metal plate with 2 odd shaped holes starts, stops and regulates the flow.
This is all well and good but in the rear half the cartridge there are 2 concentric cylinders with several holes in each. My first guess was that these cylinders are for mixing but they are before the hot and cold would mix, near as I can tell.
What do these parts do?
What is the typical failure mode?
The cartridge looks pretty good inside, like it should still work.