Overflow and drain questions

[vwmoon1]

Quick specs

72 bow front, 20l sump
single 1.5 slip bulkhead in display
1.5" drain dual outlets
3/4" return with 3/4" loc-line in tank
mag 9.5 pump
overflow/skimmer box is 7.25 long, 2.25 wide and 6 tall


It runs fine just loud. the overflow box never fills up with water, the drain sucks it out and causes a waterfall/siphon noise.

To fix this I put a ball valve on the drain and tuned it until the overflow box filled up to right about the bottom of the teeth. Then had to put a t-fitting and ball valve on return and divert flow back to sump so tank wouldn't overflow.



Now there is no noise from overflow box, but my drain is choked down because of ball valve and that scares me.

So what's the real fix here?

Do I need a overflow box with twice the length?

http://i263.photobucket.com/albums/ii121/vwmoon1/IMAG0476.jpg

pic of overflow box before I put on rear vent
http://i263.photobucket.com/albums/ii121/vwmoon1/IMAG0469.jpg

build
http://www.reefcentral.com/forums/showthread.php?t=2330769

[vwmoon1]

Did some math, my total gph with my pump is 620 including head loss.

says I need


Recommended minimum drain pipe diameter = 1.01 inches
Recommended minimum linear overflow size = 9 inches


I have

Drain 1.50 inches

linear overflow 4 inches :headwalls:


If I cut all the teeth off my box that will give me 12 inches linear overflow. and should be able to open drain valve.

What do you guys think?

[uncleof6]

A mag 9.5 won't put out 600 + gallons through 3/4" pipe. They require 1.5" pipe to think about operating on the flow curve, so you are far below that, and having problems, typical of open channel drains: The flow rate is too high for 1.5" pipe which has a ceiling around 350 gph before it starts choking. Choking the drain line with a valve is an extreme plug risk, as well as the instability of choked open channel drains, presents a flood risk without plugging the drain. The solution for needing flow rates above 350 gph - 400 gph, done safely, is a siphon system, with emergency dry back up. Reference Herbie (done correctly) and BeanAnimals drain system.