[quote=John Rumm]

You will need a little bit of play in the pipes to get the old valves
out. If they are fixed rigidly, then cut away the valve with a pipe
cutter, and use a soldered slip connection to make the last joint.


If you undo the back nuts on the underside of the mixer you'll be able to
lift the valves off without cutting any of the existing pipework. You might also be lucky and find that FULL-BORE quarter-turn valves fitted in line in place of the valves will avoid you having to add any new pipework.

Good luck.