hot water pressure feed to bath

[Richiej]

I'm fitting a new bath with a "coolfill" filler ( built into side of bath) via a shower type mixer valve recessed into the wall above the bath. The existing hot feed was on 22mm copper pipe thru to tap but the new mixer only has half inch "cylinder connectors" connectors the biggest outlet I can find is 15mm and if i used plastic with the insert would further reduce flow. could take days to fill bath on 15mm pipe.
I've been everywhere trying to get half inch with a 22mm outlet to increase the flow on my gravity fed system.
Does anyone make one? what alternatives are there. Some suggest fitting a pump just on the hot. not keen due to expense.
Help please

 

[macplumb]

Can't you put in a 22mm x 15mm reducer and couple with half inch tap connector.

 

[Richiej]

Yep that's possible but i was trying to get a feed to the bath filler in as bigger diameter pipe as poss ie22mm. I appreciate it goes thru the on valve wich will restrict the dia. a bit but can i return to 22mm again after the valve to the filler on side of bath?
The main feed is 22mm thru to the restricted valve ( about 19mm) then BACK to 22mm to the filler. Is that acceptable/allowed or even worth it.