Overflow Rating Question

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landmineyouth

landmineyouth

Gambusia
MFK Member
Sep 3, 2005
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North Miami
www.djrobriggs.com
Recently purchased a brand new Marineland 350gallon (6x3x3) with dual corner overflows. The sticker spec says each overflow is 'rated for 700gph'.

My question is, if that means a total of 1400gph with both overflows, would there be a reason to buy a pump any larger than that particular rating? Will it only push this much gph no matter what, with the current overflow setup?

I was also planning to buy a Mag 24 (2400gph) for a 300 gallon long I have with a single overflow in the middle, but since this overflow is much smaller than the marineland ones, I cant imagine it being rated any higher than 500 to 700 gph as well. Would this pump be a waste??
 
You don't want a pump that will return more water into your tank than your overflows can handle. If your overflows can't keep up with the pump, the pump will suck your sump dry and your pump will be pushing air & water (not good). Buying an oversized pump would be a waste because A. it will likely cost more $ up front and B. it will cost more money to run because it will use more electricity. But keep in mind that the 2400 GPH rating is at 0' head. The pump will likely have to push water up to about 5 or 6 feet, so it will only be capable of pushing around 1,800 GPH, not 2,400.

Check out these flow charts- http://flexpvc.com/WaterFlowBasedOnPipeSize.shtml. As you can see there is some variation in the numbers, but it will give you a ballpark as to what you can expect to see from different sized bulkhead fittings/pipe. If you want more flow you can drill larger holes (assuming it is safe to drill the glass- I would talk to the manufacturer first). Again, a larger pump will not increase your flow...you are limited by the GPH that your overflow is capable of regardless of how huge of a pump you get.

Depending on the type of pump you have, you can valve it back or create a "T" on the return line so that you are diverting some of the pumps output back into your sump. If I were in your shoes I would get a pump that does just under what your overflows are capable of draining. Be sure to account for how high your pump has to push water to determine your true GPH. Good luck!
 
Thanks for the reply, this is great information, but a little disappointing as I have 300 to 350 gallons to filter and seemingly only able to buy a pump which will turn over the tanks water 3 to 5 times as opposed to 10 like I'd perfer. I need to do some research on the plumbing and what size my drains are before answering further. I suppose if I don't want to drill glass, I can always add a canister filter onto the tank, or into the 75 gallon sump tank below the show tank to allow more filtration?
 
Alright guys help me here. My tank is pre-drilled inside the over flow with two 1.5" holes. Assuming I use them both as drains, and plumb seperate PVC returns hanging over the back of the tank, that technically gives me a 3" drain, correct?

1.5" 1.50-1.60" 1.90" 35 gpm 2100 gph 81 gpm 4,830 gph 126 gpm 7,560 gph1.5" 1.50-1.60" 1.90" 35 gpm 2100 gph 81 gpm 4,830 gph 126 gpm 7,560 gph


Double my drains there and you see I have around 4200gph. Plumbed with around 6ft overhead, would I correctly be assuming I have somewhere around 3000gph pump to purchase??
 
The bulkhead size that will fit in a 1.5" hole will depend on what type of bulkhead you go with....

If you use a flimsy cheap bulkhead, you can have I believe a 1" drain hole size.

With a schedule 80 bulkhead(all I use, since I had a cheap bulkhead skip threads), you will be down to a 3/4" drain hole.

Here is the physical difference between the two bulkheads I bought. The black is the one that failed.

311db981.jpg


f1cbbe70.jpg


24358b9a.jpg


If it already has bulkheads, and they are 1.5" inside diameter, then you can get more than 750gph out of those.
 
My opinion is that overflow ratings are grossly understated, but it's understandable why they would do that. If you run into issues, run a full siphon drain setup (Bean Animal, Herbie) and you can run a lot more flow. I've pushed 3400gph through one 1.5" pipe and 1000gph through a 1" pipe.
 
jcardona1 said:
My opinion is that overflow ratings are grossly understated, but it's understandable why they would do that. If you run into issues, run a full siphon drain setup (Bean Animal, Herbie) and you can run a lot more flow. I've pushed 3400gph through one 1.5" pipe and 1000gph through a 1" pipe.
Click to expand...

Whatever you do, don't listen to this guy! :ROFL:




jk
 
Piscine said:
Whatever you do, don't listen to this guy! :ROFL:




jk
Click to expand...

Better watch out OP, this guy will demand a tip, just for posting in here ;)
 
I gotta tip for ya..... lol



Anyway...Jose is right. A drain can flow much more when placed under a full siphon.

If you have 4 holes, I'd run them all as drains.
I'd also use 2 smaller return pumps plumbed on separate lines instead of a single larger pump. This will ensure that if you have a pump failure, your filter will still be mostly functional.
 
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