I have a traditional telephone style bath/shower mixer tap and am getting water hammer from the valve when switching from tap to shower. I have taken the valve out and it does look a bit worn although I am not getting any leaks from the O rings. I dont know if these valves are standard in these taps but the one in mine is a length of round plastic with a slot cut out half way through which takes a dogleg cam on the tap handle which lifts it up and down. At each end there are O rings and a raised cross section. I dont know if this makes much sense, if it does then what is the name of the valve and where can I get one.