P
Perfectionist
No. The PRV stays at the main stop valve. Some unvented cylinder have pressure equalization valves at the cylinder. The feed goes directly to cylinder. After the equalization valve the cold is taken off. It ensure the pressure on the hot and cold are both equal.
If there is no equalization valve fitted, then take the feed directly to the cylinder from the stop valve. Tee off at the stop valve and take all cold supplies from this. Just before the unvented cylinder you may want to tee off the cold feed and take this to the cold inlet on the shower. If pressure fluctuates around the cylinder it will do more equally on the hot and cold lines to the shower.
The shower is king and must get priority for pressure and flow. Having the separate cold line from the stop valve means you can put a flow restrictor on this line and throttle back the whole cold supply if need be. A toilet flush can influence the shower.
