Overflow box help, turn into weir?

[got2lb]

Okay I have a HOB overflow box with the u-tubes on it. It's not a commercially made unit, it's custom made but they're all basically the same.

The problem I'm having is that I have a lot of "film" at the top of the water. The overflow box has teeth cut into it right now.

I have some acrylic in the basement, if I took and cut it to fit straight across and cover up all the slots in the box to basically make a "weir" overflow would it help get rid of the film on top of the water?

Also will that reduce the amount of flow going into the overflow box? I can only run 600 gph because it only has a 1" bulkhead in it. How long of a weir do I need to handle 600gph?

 

[brackishdude]

Presuming you have a filter/skimmer in your sump, then taking more off the top (weir) will result in less film.

The box will drain however much water is pumped into the tank from the sump. Weir vs. teeth = no difference. You just want a thin water colum flowing over the top so that max suface drainage occurs.

Picture a tall skinny building. This is the cross section of the water flowing through a slit in the teeth. Only the top of the building is the "surface". Now knock the building on its side. Same crossectional area and flow, but the long side is now on top and therefore greater surface skimming.

THere is no "required length" for the weir, but the longer it is, the skinnier and taller the bulding (that is pushed over), and the greater the proportion of draining water that is "surface water". Consider that your toothed box is really just several very narrow weirs


Only the size of your return pump/plumbing determines the required flow rate through your overflow. The hole in the top of the in-tank box is not a limiter, teeth or not. Most overflows bottleneck at the Utubes (get 2 if needed) or the draining bulkhead. I suspect 1" will be fairly limiting. Drill another or enlarge the one you've go if needed.

You could put the peice of plexi over the slits, assuming you have a box that is height adjustable (the plexi will otherwise raise the water level). Or you could take out your drill and drill a hole in each tooth as large as will maintain integrity of the tooth and not have the bottom of the hole lower than the bottom of your current slits. Then take out a file/jigsaw/dremel/handsaw and saw off the top of the holes, so the "o" shaped hole becomes a "u" shape.

Edited after seeing your number of posts. Sorry if came accros as patronizing or simplistic.

 

[CoolUsername]

I agree with brackishdude's post - no teeth = better surface skimming. 600 GPH is pushing it for 1" But there is an advantage - any bubbles that form in the utube are probably more likely to push through with that flow rate. I personally think that pushing the U tube flow limit is a safer way to go in terms of bubbles. I have had my utube get close to losing siphon just because of accumulation of air in it at the top. I noticed that when I increased pump capacity the bubbles would push through.

On the flip side it only takes one snail to clog it. I would recommend putting in some egg crate or some other critter stopper, especially if do as you are hinting and remove the teeth.

 

[got2lb]

Just because I have a lot of posts doesn't mean that I know everything!

I have the skimmer in the sump. That's the first place the water hits when it overflows.

I kind of figured it would help pull some of the film off the top. I'm alreadly limited to the 1" bulkhead and the size of the overflow box. Without redoing A TON of plumbing anyway. I don't think I have enough adjustment on the inside box to cut the teeth off. I think I'm going to try attaching some plexi to the inside of the box and see what happens.

Another quick question since Mr. coolusername brought it up. I have 2 u-tubes in the overflow box and they ALWAYS fill up with air at the top of them. I have to suck the air out of it about once a week. Are you saying that if I turn the pump up a little bit it will push the bubbles through? I'm not sure if the bulkhead will keep up with much more flow???

Thanks for the help!!!

 

[spence15610]

Most U tubes are an 1 1/8" and if you only have a 1" drain then 2 U tubes are to much, try running only 1 U tube and I bet that will solve your air build up problem

 

[spence15610]

I meant 1 1/4 on the U tubes

 

[sjm817]

If you have too much flow, you can have surface skimming problems. The level in the inside of the overflow has to be lower than the outside. If the level is the same, it wont surface skim. The water has to "pour in" to the overflow.