large vs small overflows

[Malifluous]

I plan on pumping about 350 gph. Would a 12 inch overflow with two, 1 1/2 inch bulkheads be more quiet than a 12 inch overflow with two, 1 inch bulkheads?

[asm481]

A hang on overflow? I would go with a single 1 inch bulkhead O/F for 350 gph. If you are using the U tube style you need enough flow through the tube to flush tiny bubble through. I had a problem at one point with low flow through a 2 tube O/F and fixed it by increasing the flow to about 900 gph. Two 1 1/2 in bulkheads is over kill and wouldn't surprize me if it was very noisy.

[Malifluous]

This is for an internal overflow with 2 holes drilled

[sjm817]

For 350 GPH, 12" is fine for the weir. 350 GPH will drain just fine through a single 1" pipe. I'm not sure if you are matching up the number of and size of bulkheads with the plumbing. Too much pipe means lots of air has to fill the pipe. You want the pipe to be "full" of water, not air.

[Malifluous]

my plan is to have one going at full siphon (tweaked down with a valve) and the other with a siphon break that will drain any remaining water. Redundancy makes me feel safe. i also plan to use one bulkhead to feed the skimmer ans the other going the the sump.
What u guys think?

[heyfredyourhat]

From what I did and wont do again is 1.5" drain (main) and 1" drain(backup). I have about 550gph through the return, and I need to restrict the 1.5" a lot. Like sjm says "too much pipe means lots of air), Being restricted though makes it super quiet, cannot hear it at all except for the odd "grinding" noise, like when you try to spit through your front teeth...!

I also have the 1.5" drain tee'ed off to the sump and the skimmer, which is very tricky to dial in. Not sure I would gravity feed a skimmer again. Cant tell you if it works well or not, tank isn't quite ready for the LR yet.

[IPT]

I have two tanks both drilled with (2) 1" drains. One is throttled back with a gate valve and the other is a back up. Virtually silent. If anything goes awry (like the frigging snail that went into the valved overflow) the secondary takes over. When you hear noise you know something's up (but your floor is still dry ). Wouldn't do it any differently.

My weir in the 50 is 10''x2" and in my 75 a little longer (don't remember the dimensions and the tank is at my office). Same return pump (Eheim 1260). My 75 gets much more/better surface skim. 12" may be enough, but the more length the better as far as I am concerned.