HELP--Overflow won't keep up with pump

[buyitjody]

I have a question about Pre-Filter Boxes. Basically I have the following:
55 gallon glass tank
10+ gallon sump
Iwaki 20-RLT (rated approx 400gph)
Prefilter/overflow rated (supposedly)to 800gph
Problem: overflow cannot keep up with pump (tank fills up faster than overflow can drain water to sump)
Back prefilter box is 3"x10"x8" with a 'divider' that starts 2" below the the top of the prefilter box. Output is 1" bulkhead. The Pvc pipe connected on the inside of the prefilter to the output bulkhead is about 5 1/2" tall. Prefilter box starts 3/4" below the acrylic part that holds it on the tank. If we put a 1 1/8" siphon U tube from the overflow to the prefilter side without output, then it cannot keep up if the Iwaki is set wide open. If we put another 1 1/8" siphon U tube from the overflow to the prefilter side without the output, it still cannot keep up. If we move the second U tube so it goes from the overflow to the prefilter side WITH the output, then it keeps up and even out does the pump (then the pump can't keep up). If we take out the first U tube that was from the overflow to prefilter side without output, then the prefilter box cannot keep up. One thing we thought may be the problem is that the barrier is too high in the prefilter box. However, the box cannot keep up even if the siphon tube is on the side with the output. That lead us to believe that the inner PVC pip is too tall, causing the siphon to be slower?
Not sure, but really need some help if you have any ideas. This is not a name brand, but by a guy that makes them.
Much appreciation for any help,
Jody

 

[dreeves]

What kind of overflow is it? Are the drain lines to the sump of equal or greater inside diamter as the overflow? Do they have a straight shot down to the sump? No level outs or uphills?
Also, if you havent, you should have a bal valve on the outlet of your pump...with this you can regulate the output of the pump to the spray bar.

 

[broomer5]

Jody,
I agree with your conclusions.
A 1" bulkhead drainline should easily handle the flow from your pump.
It's not the fault of the drainline - it's the slow movement of water up and over the U tube is most likely causing your display tank level to rise too far.
It sounds to me as if the divider is too high in the outer box AND the standpipe is too high as well.
When I say too high - I mean in relation to the water level in the display tank.
There must be a difference in elevation of the water levels.
The outer box water level ( as determined by the height of the standpipe MUST be lower than the water level in the display tank.
Otherwise - you will not have enough difference between the two.
It's the difference between the two water levels ( difference between display tank level and outer box level ( that allows the water from the display tank - to be pushed up and over the U tube.
If this difference is small - then the amount of water moving through the U tube will be small.
If the difference is great - then you'll find more water moving up and over the U tube.
What do the water levels in your set up look like - relative to each other.
The display tank level vs the level in the inner and outer box.
I'm guessing your inner box is about flooded and even with the display tank - and the outer box water level is just slightly lower than that of the display tank.
What is the difference in the water levels in your set up ?
Here's a pic of one of my overflows showing these different water levels.
The water level in the outer box is detemined by the height of the standpipe. This overflow does not have a divider. The siphon is maintained by the water level that is provided by the height of the standpipe. In outer boxes that have the divider, the divider is there to just provide a chamber so hold water - so you don't lose siphon. Normally having the divider is a better design.
Aside from hacking away on your outer box to lower both the divider wall and the standpipe - the only way I can see to increase flow would be to lower the entire outer box down.
Is this possible with your design ?
You may have to fabricate an extension bracket of some kind.
If not - you could try to cut off some of the standpipe height, and maybe drill holes in the upper portion of the wall divider ( or cut it down as well )
The other option - spend some bucks on an overflow from Lifereef or some other manufacturer - that is of a good design.
Here's couple pics

 

[broomer5]

water levels and standpipe height IN RELATION TO the display tank

 

[buyitjody]

dreeves--It's made by a guy that sells many of them on ----, so it's a no-name brand. I don't think the problem is anything to do with water draining down, being that if we put 2 U tubes on the side that had the output pipe, the water came shooting out (made a mess doing that because it came out so hard into the sump) We do have a ball valve after the pump so we can easily service the pump when necessary, but we should not have to turn it down more than halfway...800gph overflow should have no problem keeping up with a 400 gph pump. Thanks for the thoughts on what might be the problem.
broomer--I think we will first try cutting the inner standpipe down first since that is the easiest solution. Would there be an easy way to cut holes or cut down that inner barrier some since it's kinda tight getting in there? Also, I was anticipating the problem of the pump not keeping up with the overflow. Once we get the overflow worked out, I'm sure this situation will be next. Is it ok to put a gate valve at the input into the sump so that we can regulate the amount taken by the overflow? Thanks for validating what we think is the problem. Hopefully our modifications will work. Is your overflow in the picture a lifereef?
Much appreciation,
Jody

 

[broomer5]

Jody,
I run two of these overflows on my 30 gallon.
They were made locally here by an acrylic shop that makes wet/drys and such.
I would not restrict the flow from the overflow drain to the sump with a gate or ball valve.
Some folks do - I prefer not to.