Overflow Boxes

[VelvetAirwaves]

Hello all, been looking at overflow boxes and siphon overflows for abit, does the return have to be exactly the same gph as the overflow in order for the overflow box to work? Or will the overflow prime itself such that the return gph dosent affect it? Do tell

[bkburger]

Hi, if you get a return pump that is too strong, the overflow might not be quick enough to bring down the water from the tank to sump. So you have to know how many gph the overflow box can handle.

[VelvetAirwaves]

Agreed, however doesent the overflow box/ pipe have a fixed flowrate? such that my return gph has to be the same to that of the overflow? I understand that an inbuilt overflow dosent have this problem as it is able to adjust to the water level in the tank. But as for external overflows that use a siphon, dont they have a fixed retun gph?

[diki88]

Agreed, however doesent the overflow box/ pipe have a fixed flowrate? such that my return gph has to be the same to that of the overflow? I understand that an inbuilt overflow dosent have this problem as it is able to adjust to the water level in the tank. But as for external overflows that use a siphon, dont they have a fixed retun gph?

if you know how much ur overflow is rated for it's just getting a return that is roughly the same after factoring in head loss.

here's a head loss calculator from rc which I find rather useful. http://www.reefcentral.com/calc/hlc2.php

If your are unsure about how much can it siphon out, get a strong return pump and fine tune by using a control valve.

Hope it helps.

[VelvetAirwaves]

Thats pretty helpful bombom thanks. Fine tuning is one thing, however, wouldnt evaporation rate of the water then again cause the system to go haywire on either side i.e the siphon side and the return side? From what i see, If the siphon/external overflowbox has a fixed flowrate, then fine tuning would be an option, however, if the siphon/external overflow does not have a fixed flowrate(from what i see in the diy section) then fine tuning would not work because if the level of water in the tank decreases, the rate of siphoning decreasess as well no?

[diki88]

correct me if im wrong, evaporation rate would affect your sump's water level, usually in the return compartment to drop instead of your display tank.

the water level in your dt would remain constant if siphon out = return in.

btw im using a diy overflow 25mm pipe i got from one friendly reefer here. initially using a 900l/h pump for just one pipe and it wasnt enough as the water was being siphoned out more than it was coming in. had to change to a bigger pump to accomodate it and fine tuned to equalize both siphon and return.

hope other experienced bros could help you out here as im rather new as well.

[bkburger]

Have both return and overflow fix with control valve, and should be fine, if pump too weak, tune the control valve at overflow to smaller, if pump too strong, than turn the valve on the return to smaller.

Yes water evaporation rate would affect your sump's water level, not in the main tank. I am also using a DIY 25mm overflow pipe.

[Nastro]

Just top up water in the return

[VelvetAirwaves]

Just built my overflow unit, shall post some pictures this weekend once im out of camp.

[Terryz_]

There is actually a table that match the flowrate to the pipe size... I am using that and no problem so far almost a year liao.. and it is self priming...

[Jameshong]

There is actually a table that match the flowrate to the pipe size... I am using that and no problem so far almost a year liao.. and it is self priming...

Hi Terry,

Where is the table? Mind sharing here?

[VelvetAirwaves]

FInished the build on the overflow pipe, however after testing, the flowrate is really minimal, im using 15mm pipes. Plus is there anywhere that sells the valve for a one way airflow?

[bkburger]

Hi if your valve on your overflow was turn on maximum and you still find the flow small, than the problem is your pump rate too low.

Can tell how big is your tank and what rate pump you are using?

[VelvetAirwaves]

pump return is 1400l/h so i guess i need to tone it down a little.