water height in overflow box

[Chad]

Just a quick question.. what determines the height of the water in the overflow box?

If I do a herbie style overflow, matching the overflow with the return, would the height ever get beyond the overflow hole?

I am a bit confused because I do not know how high I need to make my box, or how small I can make it. Any suggestions out there?

[sphelps]

usually the standpipe determines the overflow water level, and it should be just slightly lower than the tank water level as the closer they are the quieter it will be.

For the herbie style you don't use a standpipe and use a gate valve to adjust the water level in the overflow box. For this style you need a back up drain in case gate valve gets clogged or the flow rate changes. Usually the overflow box has two holes, one is left open from the bulkhead and the back-up usually just has a long pipe that extends near the top of the overflow. The gate valve is adjusted until the water level in the overflow is just below that pipe end.

I've always done the herbie style a little different and use a standpipe rather than the back up tube, it allows a little more freedom in adjustment as if water goes into the backup it won't be noisy. You can also get away with using a standard ball valve rather than a hard to find, expensive gate valve.

The water level in the tank will be about 1/4" -1/2" above your overflow box depending on it's size and flow rate.

[Chad]

Any chance you have a photo of your overflow box?

I got the general idea. I guess what I am after, is I'd like to make the overflow box as small as possible.. so, I have a max return of 200gph.. in a 18 by 14.4" tank.. Using 3/4" piping.. I want to get the overflow box height as tiny as possible, but I have seen so many peoples overflow with 2 or so inches of water ABOVE their normal overflow drain.. with still an inch of so more before it ever reaches the emergency. So, what causes the height above the real drain to be higher than the actual inlet? I would think if it was a matched flow it would never be higher.. am I just cookoo? and not seeing something?

Thanks for the help!

Chad

[KingTitan]

where is the hole drilled on the tank for the pipe?

[Chad]

I have not drilled anything yet.. I am trying to understand this first before I go drilling my tank.

I will be used two 3/4" drains. My idea was an 90 degree elbow down with slots cut in it so it will butt up against the bottom of the overflow box.. also providing a screen. The other drain will be 90 degree elbow up with a small pipe that extends I figured, 1/2 an inch down from the top of the overflow box.

But, since I don't understand what will control the water level in the overflow box, I am not sure if I will have enough height. now, I get the gate valve will back up the drain so it is even, thats no problem.. got it! :-)

If someone can give me this in a K.I.S.S. format I will be very happy :D

[sphelps]

I posted some pics here (http://canreef.com/vbulletin/showthread.php?t=42414)