Hi there,
If I pump water up a 30 metre high hill using a the same pump (say 70lbs at the pump) but I use 2 different sized pipes like 50mm and 90 mm poly pipe both 600 metres long, which pipe will flow more?
And at the bottom of the hill with gravity pressure flowing water back the other way, say there is 30 psi static pressure at the bottom, is there more force at the bottom of the 50mm pipe or the 90m pipe?
If say there are 3 square inches in one pipe and 6 square inches in another pipe does this then mean that at 30psi there is 90 lbs force in the first and 180lbs in the other?

If you are able to move water 30 m up with that pump at all, then 90 mm pipe will definitely be much-much better than 50 mm. there will be more GPH. The question is what the exit pressure is for that 70 lbs pump? The water column of 30 m height creates about 40 psi. If 70 lbs are applied to the 50 mm pipe directly, then you will have an about 20 psi pump, but I guess these pumps are designed to deal with higher pressures.