@Maxx470
I made a similar post on this subject a while back.
After much experimentation, I found that restricted bore isolation valves, flexi hose and the wrong taps can all contribute (more than one would think) to the flow coming from the tap. My low pressure hot feed (bath) went from 4l/m to 16l/m by changing a few items.
See my post here,
https://www.diynot.com/diy/threads/ball-a-stop-isolation-valve-easy-to-swap.474279/
That was for a first floor bathroom with mains cold and gravity hot.
After a lot of looking about and research, I found that a lot of the pressure measurements on taps could be misleading. When a lot of modern taps say "suitable for high and low pressure". Often it means that yes....they will work with low pressure, but when you look at the flow rate, it is very low.
Anything with a quarter turn or a half turn is not really suitable for low pressure/gravity fed. This is because they all use ceramic washers which have such small holes, the flow is severely restricted. Some are better than others, but only the full turn taps (multiple turns) with rubber washers are suitable really.
For a kitchen tap, something like this (which states compression valve and full turn operation) is the kind of thing you are looking for.
https://www.screwfix.com/p/swirl-traditional-sink-mounted-mono-mixer-kitchen-tap-chrome/27813
In terms of isolation valves, remove those on any feed that is gravity fed (hot only for mine). Or if they are restricted bore valves and you want to keep an isolator, swap it out for a full bore isolation valve.
As it is a monoblock mixer, you may find that in terms of pipework the widest bore you can manage is 12mm with copper pipe tails. If it is a really low pressure system and the flow is that poor I would certainly swap out the flexihose, at least for the gravity fed ones. If this is an issue, look for the widest bore flexi-hose, 10mm is probably the widest you can get.
If you like more nerdy calculations I found this site very informative.
http://www.johnhearfield.com/Water/Water_in_pipes2.htm
For example, 1m of 10mm pipework is equal in resistance to 7m of 15mm pipework.
So in my view, any little helps.
Much to the surprise of some on here, the flow from my bath tap increased massively with all the changes I made.
