Is this right? (question about flow rates for a mag 12)

[hmt321]

I bought a Mag drive 12 for my 125 gal tank, it will deliver 1100 gmh at 4.5' head with a pipe size of 1.5"

1.5" pvc is big, to big to use for a return from sump to tank, to get around this i will reduce the 1.5" to two 3/4" returns. but i sat down to do a little math,

the volume of a 1' piece of 1.5" PVC is 66.61982971" cubed
(value of Pi * Radius squared * 12")

the volume of a 1' piece of 3/4" PVC is 16.65495743" cubed
(value of Pi * Radius squared * 12")

so by using two 3/4" PVC returns I am cutting the volume in half??
(two 3/4" PVC return lines would give a volume of 33.30991485" cubed for a 1' section)


what is really perplexing is that to get the return line up to 1.5" i have to use a 3/4" to 1.5" bushing, the pump outlet is 3/4" threaded

I have never had a good head for fluid dynamics, but it seems to me that the 3/4" outflow of the pump would be the restricting factor here.

I was hoping to get around 900 gph out of this pump, but i think that i will be more likely to get around 600 gph.

question: is this estimate accurate? does anyone actually use a 1.5" return pipe in there aquarium?

thanks

[Gumby131]

i got lost second paragraph

[hmt321]

what i am asking is:

does anyone use 1.5" pvc as a return line?

does anyone know approximatly how many GPH this pump will deliver, if i split a 1.5" pvc pipe into two 3/4" pipes?

thanks

sorry the 1st post was so muddy