"BenignVanilla" wrote:

I have been thinking today about our conversation about pipe sizes a week or
so ago, and I have decided I am still confused. If most pumps have 2-inch
fittings, what good does it do to have 4-inch pipe everywhere else? Isn't
the 2-inch connection the limiting factor?

Yes, it is. Being at the pump, there is pressure available that can
over come (somewhat) that restriction.

Keep in mind (pi-r-squared) that pipe capacity increases faster than
diameter, so that you don't need to double the diameter to double the
flow capacity.

Any thoughts?

IMHO, on pressure piping (from the pump) you don't need to go more than
one pipe size up from the pump outlet. Unless you have a very long run,
or a lot of bends and turns, with a lot of resistance. So with a 2 inch
pipe output, that would be 2.5 or 3 inch pipe.

Large (3-4"+) is needed more for gravity flows, and such where you don't
have the flow rate you do with a pump. Not to mention debris.