The pressure will remain the same in any pipe connected to the supply set
at
3bar and the only thing that will change is the flow rate. The only thing
to happen when you increase the pipe diameter, is that the water takes
longer to flow through it in accordance with the increase in volume of the
pipe and would seem as though you had a reduction in the pressure, but in
actual fact the water is still being supplied at 3bar.

Thanks what I meant - but didnt explain very well.

Thanks