ceramic disc
mixing valve in a faucet: ok I will assume you are refering to a shower valve, that is the only faucet w/a mixing valve: shut off the hot and cold water. cut out valve or unsweat it. clean and flux new valve, pipe and fittings(if used) sweat in new valve
A tub faucet acts as a shower and can be used to bath in the bath tub. It is a pressure valve which makes the flow of water through it constant and gives a nice shower.
Turn the water off to the faucet. Remove the handle. The top of the faucet should unscrew to get to the ball valve. Replace the valve and gaskets then reassemble the faucet.
If the faucet contains the re-direction valve (closes off the water from the faucet and redirects the water to the shower head) you need to rotate the faucet counter clock wise to unscrew it from the plumbing and replace it with a new one. Take the old one to your local box store and they can match it up for you.
A trim kit is just the outside parts that you see. This will make you faucet look better, but it wont affect the function of your old valve. If your shower valve doesn't work right, replace it.
pressure regulator valve gone bad . stem problem or seats in faucet
You need to buy the extractor tool from Home Depot.
According to the Architectural Graphic Standards The height is 42" from the shower floor. and the head should be between 65" and 78", I usually set this height at 74"
Seperate valve for outside faucet turned off, broken valve stem inside of outside faucet or handle stripped at faucet.
If it is a Monticello Lav, you should be able to grab it with pliers and pull it out. Make sure you pull it smooth and straight. If it is a shower faucet, do the same thing, just be sure you are careful and do not rip the shower valve out of the wall. Just did one of those today, WITH a diverter stem!
If you mean shower valve, screws are for shower valve coverplate.
The average is 16 inches, naturally there are some lower and some higher, according to requirements and design.