Water filter setup - 1 1/4 inch pipe to 3/4
You are (and may not realize if you did not pay attention in geometry class) talking about a nearly 2/3 reduction in pipe size (area/cross section) when you go from 1-1/4&quot; to 3/4&quot;.
Area of a circle = Pi r squared. 1.23 .vs. 0.44 square inches for the pipes under consideration here.
That will definitely have &quot;a negative impact on pressure and flow&quot; as compared to keeping it at 1-1/4&quot; throughout.