3 way diverter pipe sizes

[kls]

Hi,
all advice greatly recieved

I have a gravity fed non pumped hot/cold water supply to my bathroom
I am fitting a low pressure suitable 3 way diverter which will feed my bath filler a static shower head and a hand shower.
I will use the original water supply from my bath taps
These are 22mm pipe
My real question is,
Do i continuue the 22mm pipe directly to the diverter inlets and the use 15 mm outlets to the hand and static shower and 22 mm to the bath filler or do i reduce the size from 22 mm to 15 mm to the inlets on the diverter and use 15 mm for all the outlets.
Or another combination
Can someone advise please.

Thank you

 

[WHPES]

The rule of thumb for gravity systems is to keep as much in 22mm as possible before you reduce down, though sometimes it's impractical. When you reduce down you increase viscous drag on fluids passing through. Try to use slow bends as opposed to elbows. Fortunately with modern high pressure plumbing these issues are rarely encountered today.