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Old 02-25-2011, 06:24 PM   #1
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Overflows... GPH versus return pump etc

Hi folks,

Please take a look at this overflow:
YouTube - CS Overflow - Overview and Installation

It has a connection for a small pump which keeps the siphon going, so keep that in mind.

My question is this:
This has a flowrate of whatever gph, but my return pump can be anything BELOW that gph and things will function, right?

If the siphon is never lost then this overflow would stop and start depending upon the water level being above it's entry line, right? So basically as long as I send water back below the GPH of the overflow it shouldn't be possible to overflow the display tank, and as long as the waterline drops below the overflow before the sump fills, it shouldn't be possible to overflow the sump either, right?

I'm guessing that with evaporation the water level of the sump will fall, while the return pump SHOULD always keep the water level of the display tank at the overflow boxes level...

Am I understanding how this works correctly?



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Old 02-25-2011, 06:30 PM   #2
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Yeah, you pretty much have it the whole concept down.

Typically, overflows that have more than 1 U-Tube we try to closely match the return pump GPH to the overflow capability to prevent one of the siphon U-Tubes from collecting air (which does happen, I didn't match mine properly and I have to watch things all the time).

With the pump to help maintain the siphon, you're less likely to fall into this scenario, however, from my experience there's 2 things to be mindful of:

1) the siphon maintenance pump failing
2) believe it or not, when the siphon U-Tubes lose siphon and fill with air, the float up in the water. If this were to occur, the pump would not be able to reestalish the siphon, and if you're return pump is greater than what 1 U-Tube can handle the result is an overflow.

Personally, I will never again utilize a HOB siphon style overflow, because of these types of issues (I have overflowed my tank on more than one occasion. once I was out of the country when it happened and my poor wife had to call a really good LFS for help).

My next opportunity I will reset my non-RR tank by drilling and installing gravity feed overflows, similar to those from glass-holes.com, but that's just me.

In the DC Metro Area? Check out GWAPA and WAMAS
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Old 02-25-2011, 06:32 PM   #3
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yep,spot on,but if the small pump fails then the syphon could be lost,which is why I would reccommend the eshopps overflow box.
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Old 02-25-2011, 06:43 PM   #4
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Thanks! And thanks for the negatives too.
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Old 02-26-2011, 05:44 AM   #5
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The one thing that is being overlooked here is that the sump should be designed to accommodate the excess water in the DT should your pump fail and the DT should have enough room to accept the water in the return chamber of your sump should the siphon fail. If everything is properly designed neither your sump or DT should never overflow.
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flow, gph, overflow rate, overflows, pump, return pump

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