hob overflow and pump

[kdogg85]

I am helping one of my friends set up a 125g tank. He asked me about an overflkow because he wants a sump and fuge like mine. His tank is not drilled and he purchased a 1600gph overflow. He has a 55g for a sump and a 30g for a fuge. I drilled a 2.5'' hole in the sump and fuge and have them connected(sump level gets to around 75%, then dumps to the fuge and then back to the main tank. My question is, what sized pump should I use? I want to ask because I was thinking with 49'' of head(the distance from where the pump is to the top of the dt) should he get a pump bigger than the overflow with a tee and valve in the return pipe to equalize flow or a smaller pump and let the water rise and drop?

 

[melosu58]

Moved to General Hardware and equipment discussion.

 

[BigJim]

You should never have a pump that can outflow the overflow. That leads to floods. Once the system has stabilized, the water shouldn't rise and drop. It should be at constant levels.

 

[kdogg85]

So the pump should be undersized or get one as close as you can to the overflow? I had thought of doing what I done for mine on the return(a tee with a valve that lets some of the return water go back to the fuge to equal the overflow) The pump on my tank is capable of outflowing the overflows on mine and that trick got me setup perfect.

 

[krap101]

It basically doesn't matter what sized pump you get, as long as it's less than the rated gph of the overflow. I understand it as if as if the pump slows down for some reason, less water gets pumped back up, so the water level is lower >> less water drained through the overflow. That said, you need to pay attention to head height, and also... don't go thinking that I meant for you to get like a 120 gph pump . I'm unsure on saltwater requirements, but I'm guessing 1200ish or so would be good.

I forget, but for the pvc type overflows, there needs to be a siphon breaker in case the power goes out or you'll end up with like 50 gallons of water on the floor

 

[BigJim]

You could split the flow as you suggested, but still keep the pump flowrate below the overflow flowrate as a failsafe. You never know when someone might "help" you out by closing that valve to stop your leak.

Aim for a pump that will give you 10x turnover per hour. For a 125g, 1200-1300gph would be good. Check out the pump curves to find a pump that will flow those numbers at your particular head pressure.

 

[kdogg85]

I read the valve was to equalize flow and to protect the pump. The article said doing that would let the pump run as unimpeeded as possible to prevent from burning out too early. I have pre-drilled holes and the hob overflow thing is still fairly new to me.

 

[corrado33]

Yes the valve will protect the pump. If you tried to simply restrict the flow of the pump with maybe a smaller diameter pipe or something, you'd put undue stress on the pump, and the motor would burn out. What people are saying is that if you buy a pump that gives 1200-1300 GPH at your head height (It'll be rated higher, but you gotta look at the head height calculations, there are some online), then you won't need a T with a ball valve, because your pump will never be able to "outflow" your overflow and your tank will never overflow.

 

[David S]

I don't think you need this T,If you look in the specs on most pumps used as a return pump they show all the different flow rates per head as long as you are within these parameters the pump will be fine,I personally wouldn't use the T just make sure the pump is the correct size for your overflow,what type of box are you using,I wouldn't use any but the syhon pipe type.and also drill a hole in your return pipe in you dt just below water level as an air break otherwise your fuge will overflow within seconds during a power cut.