Greg's 75g

[daplatapus]

Originally Posted by WarDog

Yeah buddy, thats the way to do it correctly. That wye you got set up is improper venting practice to the extreme. Too much back pressure causing an air flow bottleneck. Great diy project!

Looks great! I was expecting a lot worse from your description.
In the strictest of air flow practices, if those are 4" lines you'd need a 4"X 4"X 6" Y for it to work as you'd intended. Just use Pi R squared to figure out the square inch of 4" round (X2 for 2 pipes running into one) verses the size you want to run it into.
I highly doubt those fans are pushing the limit of a 4" pipe though. A 10' run (including friction loss for elbows) at .05 inches static pressure loss, a 4" pipe can flow 45.8 CFM. That's pretty low static pressure, but I'm not sure what pressure those fans can push without cavitating.

A thought to also consider... I have had some instances in a somewhat similar application of 2 fans feeding from a common plenum. One fan started a few seconds before the first and from the suction it created in the plenum it pulled air backwards through the second fan and the blades of the second started rotating backwards. Sometimes the motor's are not powerful enough to counteract that reverse spinning and they just sit there cavitating until they either burn up or shut down from overheating. What fixed it for me was just installing a baffle between them, making 2 separate plenums.