The brand is Moen
It' a single handle, left for hot, right for cold.
No other valve in the tub.
Home is hard water, there is no water softener
Home is 9 years old
I don't know the model # of the faucet
A 7 inch diameter chrome plate covers the valve.
Hope this helps, Thanks

Call Moen at 1-800-BUY-MOEN. Describe valve and get free replacement cartridge.
Remove Moen emblem on handle with sharp pointed tool.
Remove handle, remove chrome cartridge sleeve, just pulls off.
Remove cartridge retaining clip, small horse shoe clip.
Remove cartridge, (reinstall handle and pull)
Turn on water briefly to flush out valve.
Install new cartridge. Install with cartridge in open position so that air trapped in valve can escape as you push cartridge in.