Flow thrue PVC is this true?


New member
"Your system will only flow as much as the smallest pipe can handle. If you run 1.5" down to a 3/4" you are basically using a 3/4" system. The only difference would be less friction loss and maybe less loss through the 1.5" fittings."

Is this statement basically true.? I have a dual 3/4" return... .. would I get any benefit from running 1.5" as close to the 3/4 bulkhead as possible?


New member
So you run 1.5 to to a "T" and then to 3/4" bulkheads? If that's true you're talking about reducing:

for 1.5" pipe the flow area is:
r=1.5/2 PI*R^2= 1.76sq inches is

for two 3/4" pipes the flow area is:
r=.75/2 PI*R^2= 0.44. Doubling makes .88sq inches

So you are reducing by about 2x. Make sure and T using the 1.5 and then reduce to 3/4" on both sides. Otherwise you will restrict to 0.44 inches if you T using the 3.4 inches. This will double your potential flowrate.

Yes shorter is better in the 3/4.


In Memoriam
"would I get any benefit from running 1.5" as close to the 3/4 bulkhead as possible?"

Yes, it will help. Many people run 1" or 1.5" plumbing (if you dont have space for one 1.5" pipe, then two 1" works nice) up until the bulkheads, and then reduce to 3/4" nozzles for some extra velocity. The smaller restriction should be as short as possible at the end of the larger pipe... the longer that the water has to travel these smaller pipes, the more it will cut down the flow.


Make my Funk a P-Funk
I agree. I am doing a very similar thing because my tank was already drilled for 1" drains when I got it, but I am running 1-1/2" pipe except for about 6" at the bulkheads