Help on water height going over, overflow.

[Chad]

Well, I am doing the Herbie style overflow, just a single gate valve on the overflow end to adjust the water height so it is even with the flow from the return pump. I have spec'd the return pump to so it has a max of 200gph after factoring in head pressure. The tank is only a 34gal cube, I think 200gph should be plenty to service this size of tank. All the other flow will be from the closed loop I am putting in.

[Skimmerking]

if your tank is 24" high the over flow should be around 22.5 high so 1.5 " from the top down if that helps so your coast to coast should be 1.5 " from the top down

[Chad]

why would it be necessary to have the overflow 1.5" from the top?

[mark]

Theres' two places that can help you (here) RC drain calculator. You enter the gph and it gives the weir length with about a 1/4" over the weir lip. Other place is on RDO (download) for their Overflow calculator spreadsheet. It's for a slotted weir but if using a straight weir put number of opening as 1. Can easily play with the variables to match the height you want against flow and length.

It all seems to go back to Bazins formula Q = 0.66 x cB x (2g)0.66 x H1.5 http://www.aquatext.com/calcs/weir%20flow.htm and crank it out

[Skimmerking]

Originally Posted by Chad

why would it be necessary to have the overflow 1.5" from the top?

No chad what I was saying is the top of you box would br around 1.5 " below the top of the tank.

[Chad]

Originally Posted by asmodeus

No chad what I was saying is the top of you box would br around 1.5 " below the top of the tank.

I understand what you mean. I am just not sure why it needs to be 1.5" from the top of the tank. If there is such low flow going through the overflow and it being coast to coast, I would think I should be able to have it much higher..

I had figured to put it around 3/4" from the top, so I do not see the water line.