Ballast tech question

[holiday13]

Well I finally finished my system but ran into an issue. I am running 4 750gph aerator pumps in line in a single manifold that is conected to a 1.5" thruhull. The problem is with all 4 pumps running pump 1 and 2 are starving pumps 3 and 4 of water. Therefor making my system not as effective as I hoped. I had used 1" id pipe for the manifold thinking it would hold enough water, but I was wrong. Does anyone know where I can get a flow rate vs. pipe diameter chart? Before I jump right back in and try something else I am thinking I should do some more reseach . I need to use the old carpenter saying this time, "measure twice cut once".

Second question, the way I ran my system was to standard launch pad sacs, I ran the input to the rear of the sac on top, a vent line to the front top of the sac, and teh drain pump connected to the bottom rear. What was weird was the sacs filled to capacity but never pumped water out the breather. Should I have my fill and vent reversed? I thought put the vent at the highest point but that did not seem to work too well. If I pressed on the sac hard enough it would flow water but the pump would not push out on its own. Or is this just due to the fact that I am using aerator pumps and they just do not have the snot to push the water on, I though they would though.

Thanks for any help in advance!

[downsideup]

A 1.5" pipe has approximately the same cross sectional area as 4 .75" pipes. That's 1.76 sq. inches. A 1" pipe is only .785 sq. inches. I believe that a 1.5" manifold should be fine. I used a 1.25" thru-hull and manifold for 2 of the same pumps. I drain back through the fill pumps and the same manifold and thru-hull. I don't know about your vents, though.