# help me understand overflow, flow rate, pump for sump



## chiroken (Sep 25, 2007)

I just am not having this sink in, please clear this up for me! I have spent tons of online time researching sumps but these parts have not come clear for me.

I'm looking into upgrading my freshwater 90g to a 135 or larger and will go to a sump for the 1st time. I will build the sump from a glass tank and have an inlet chamber, 1-2 media chambers, + the pump chamber with heater. I'm not getting how to determine how many gph will flow thru my sump. I got to thinking today when looking at 2 external overflow boxes (CPR?) (my preference is to do internal). The first one had one 1 1/2" bulkhead rated for 1600gph and the other had 2 1" bulkheads for a total of 1500gph. Going way back to high school math I found that the 1 1/2" outlet had more surface area, therefor more flow, that 2 1" outlets.

If I plan on having 2 outlets, either 1" or 1 1/2", how do I figure out the flow rate into my sump? It has something to do with the depth of the water in the aquarium, or the distance from the top of the durso standpipe to the sump chamber? The higher the fall, the faster the fall, the higher the gph flow rate? How is this calculated? How do I create my desired turnover rate? I guess I'm not getting how you can manipulate flow rate when the outlet size remains constant...how do you "slow down" gravity?

I've read that the strength of the pump will determine flow rate (I understand pump ratings vary based on how high you are pushing the water back up to the tank)? I don't get this...isn't gravity gravity and water will run downhill at a constant rate when the aquarium level stays constant?

I can't get how the sump doesn't overflow if the pump doesn't at the very least push out as much water as flows in via the aquarium outlet. Unless it is because the reserved volume of the sump is greater than the volume of water in the plumbing and the volume of water from the aquarium surface down to the overflow box level. This is the safety net in the event the pump quits (ie power outage).

And why are there 2 returns of 1" when the pump's outlet is 1". Why not just have 1 1" return? If you start with 1" outlet, how does splitting that into 2 1" outlets at some arbitrary point affect anything? I'm not clear why it seems to be suggested to have 2 returns entering the tank rather than just 1 (unless it is just to have 2 re-entry points to create more water/tank disturbance).

For a guy that excelled in the sciences this has got the best of me....anyone make this clear as mud for me? OK, hope this post doesn't leave you now completely confused with my questions!!! :-?

Thanks.


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## fox (Jun 11, 2009)

Where to start ...

What type of fish do you plan on stocking, that pretty much determines your target range for turnover. If you stock small fish with light bio load shoot for 5x's turnover. If you stock messy large fish with high bio load shoot for 10x's turnover.

Size your drains to meet this turnover volume demand, this is the amount you will be flowing thru the sump.

Size your return pump to be a bit larger than this number when head is accounted for. You run what you brung and if yer pump is undersized well thats all she wrote, if it is a bit oversized you divert the excess volume back to the sump or restrict the flow back to the DT if it's not a positive type displacement pump.

The number of drains and number of returns do not have to be equal in number but more importantly equal in flow capacity _AND_ since the return to the DT is under positive pressure you will want to drain more quickly than you supply back to the DT. This is why you have larger or more drains than supply. Main objective is to not overflow the DT.

You fill the DT until it starts to overflow into the sump. Mark the DT at this level, this is _power off_. Measure the volume from this level to the top of the DT and this is the design size of your pump chamber volume. Try not to design a pump well that is too small since this is where evap is noticed or too large ... if a problem were to occur with the drain you want the pump to cavitate before the DT overflows.

There is more to take into consideration such as _power on_ sump level and _power off_ sump level, mech chamber such as socks or pads, bio chamber, sump or wet/ dry design. I would suggest you peruse the web and visit a few LFS to see sumps in operation before getting in too deep. :thumb:


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## chiroken (Sep 25, 2007)

Thank you for the reply. The plan will be Malawi cichlids, medium to heavier stocking.

How do I correlate drain size to turnover demand? Is there a basic formula to figure this out? 135 gallon tank minus stacks of rocks, gravel etc. leaves me with an easy number of ~100 gallons to work with so my target is to move 1000gph.

So by oversizing intentionally I will plumb a T into my return, with one line running back to my pre-filter section to again filter it? I have seen this type of plumbing many times, usually running into a refugium in salt water systems where the pump is situated in the middle chamber.

Type of filtration? Don't think I'll go wet/dry. I have been thinking of the sump housing a course and more fine floss, bioballs/pot scrubbies/ceramic rings and also nylon bags of crushed coral. The crushed coral currently sits on top of the foam pads in my aquaclear 100's.


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## cantrell00 (Oct 30, 2010)

> How do I correlate drain size to turnover demand? Is there a basic formula to figure this out? 135 gallon tank minus stacks of rocks, gravel etc. leaves me with an easy number of ~100 gallons to work with so my target is to move 1000gph.


Rule of thumb is a gravity fed 1" line will flow @ ~750 GPH. Most 6' tanks come with 2 overflows X 1" & therefore a overflow potential of 1500 GPH.

What regulates the flow more than anything else is the capacity of the pump(s) less friction loss & head pressure.

Is the tank you are getting drilled with internal overflows? If so, buy a pump rated @ 1000-1300 GPH @ 6' of head pressure. Put a ball valve on the return so that you can regulate the return flow.

For the return lines, make sure they are at the surface of the water column. That way, if you have a power outage, the siphon will break before overflowing your sump. DO NOT RELY on check valves. They will fail eventually.

Here is a thread to me building my wet-dry for my 180... Down towards the bottom.

http://www.cichlid-forum.com/phpBB/viewtopic.php?t=225411&postdays=0&postorder=asc&&start=0


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## paradigmsk8er (Apr 13, 2009)

Also, FWIW....most of the "noise reducing" drain pieces (hofer gurgle busters, stockmans, dursos, etc) end up reducing flow for the drain somewhat...not sure why btu in my experience this is how it has ended up

Also, oversizing your return pump works because you can always dial it back with a gate or ball valve but realize that you increase noise and heat typically when doing so.

There are a LOT of variables....you can plan plan plan but usually everything changes once you throw it all together and try it out..so be prepared to fine tune for a little while


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## chiroken (Sep 25, 2007)

@ cantrell00: Great thread you posted. I believe it stated that your two 1 1/2" drains gave ~750gph and here you stated that 1" drains gave ~750gph. Is it basically the same for both? Doing some math I was shocked to find that one 1 1/2" drain has more area (within the circle) [1.77 square inches] than two 1" drains combined [1.57 square inches].


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## prov356 (Sep 20, 2006)

Check out the drain/overflow calculator here. 1" drain does 600 gph. I've found this to be true in my own setups. I think a 750gph rating from the overflow manufacturer is a bit amibitious.

Your gph through the sytstem is determined by your pump, but restricted by plumbing. For a 135, two 1" overflows is about perfect. That'll give you 1200gph, give or take.

Now just find a pump rated to push 1200 - 1500 gph at 5' head or whatever the highest vertical point it has to push the water. If the pump pushes more than the drains can handle, you can throttle it back.

I think you're overthinking some of this. If the pump is pushing uphill at 1200 gph, then you need drains that will allow that amount of water to flow downhill unimpeded by restrictive drains. Two 1" drains will do that. Forget about gravity. It's only confusing things. If the pump pushes more water up, then that water doesn't need to flow faster downhill, just more of it needs to flow. Think of niagara falls after a heavy rain. More water flows over the falls (so higher gph) but it doesn't get from top to bottom any faster. More can flow because it's unimpeded. Now if you dammed up the falls, less water or gph, but what gets through still goes from top to bottom just as quickly. Now that water builds and backs up and may cause problems, just as in your tank. If the water can't drain quickly enough because the drains are too restricive, then it backs up and overflows the tank. So, no harm in oversizing drains, just undersizing them. So it's ok if one point, say the durso, is 1.25" while the rest is 1" as long as that 1" will handle and allow to drain what the pump pushes up into the tank.

If the pump doesn't push it up, then there's nothing to flow down, so no way that the drain can out compete the pump return. If the pump's output was cut in half, then the drains would only be running at half capacity. Only half the pipe would be full of water. There's no reason for you to worry about slowing anything down. There will be more air in the drain line when the pump pushes less than what the drains can handle.

Regarding the 1" fitting on the pump vs two 1" drains. Water is under pressure when coming from the pump. It's not when draining. A 1" drain can handle 600gph, but when water is forced through, it can handle more. If you use a garden hose to drain a pond, the water will flow more slowly than if you hook that same hose up to a faucet and turn it on full.

Hope some of this helps.


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## RRasco (Aug 31, 2006)

prov356 said:


> I think you're overthinking some of this. If the pump is pushing uphill at 1200 gph, then you need drains that will allow that amount of water to flow downhill unimpeded by restrictive drains


This. The amount of water draining will be equal to that which is fed from the sump. That's the beauty of overflows: no flow = no drain. If you make sure your drains can accommodate the max flow rate of your pump, you're gold.


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## cantrell00 (Oct 30, 2010)

Thanks prov356.. Correct, 1" = 600, 1.5" = 750 - Gravity fed.


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## fox (Jun 11, 2009)

chiroken said:


> How do I correlate drain size to turnover demand? Is there a basic formula to figure this out? 135 gallon tank minus stacks of rocks, gravel etc. leaves me with an easy number of ~100 gallons to work with so my target is to move 1000gph.


There are a few tables out there with suggestions to how much a certain diameter pipe will flow under gravity. You need to take into consideration initial minimum vertical drop and plumbing techniques. 1"ÃƒËœ == 600gph, 1.25"ÃƒËœ ==937 gph, 1.5"ÃƒËœ == 1350 gph ...

For instance 1"ÃƒËœ pvc is said to flow 600GPH but some here myself included get ~900 GPH using proper plumbing techniques with 1"ÃƒËœ thinwall pvc durso's. 600GPH is a base line and if you use enough 90Ã‚Â° elbows expect less than that or 90Ã‚Â° sweeps mebbe more. YMMV

Work out your drain(s) for say 10x's turnover using internal bulkheads or HOB CPR, then shop for an energy effecient pump to meet that demand. The sump is just a place for the water to go before you send it back to the DT, what you do with it while it is there is where all the maintenance takes place. KISS and you won't need to tend to it too often. Easier on the knees :wink:


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## Piper (Mar 3, 2011)

My 125G will have a sump. I have a CPR 102 rated at 1200 GPH. The sump pump is a Mag 9.5 (950 GPH). The pump can not push more back up than is drained so it will stay balanced if the water level is correct. I will start the system with the power off and fill the aquarium until the sump pump return chamber (which is much smaller in volume than the total sump volume) is full. At this point the water level should be in balance more or less. As water is pumped up - tank fills and starts to drain through siphon again.

Remember on the CPR overflows - they do not use siphon tubes but a chamber which starts full of air. There is a port at the top to place a suction line. An aqua lifter will pump the air and water in very small volumes to create the siphon action if the back side and front side of that chamber are full of water. Here is a video explaining this....


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## chiroken (Sep 25, 2007)

THANK YOU!!!! The Niagara Falls analogy did it.

How much you can pump into your tank is limited by how much your drains drain. Pump volume, gph, will be limited to the maximum amnt of water that can drain away. If you pump more than you drain, exceeding your drain capacity, you overflow your tank. As long as your sump resevoir volume is = or > the volume in your tank measuring from highest water point to the siphon break, plus plumbing volume, your sump doesn't overflow (power outage)

Is this basically it?

This is me converted from dazed and confused :-? to wearing my "I'm proud of myself smile"


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## prov356 (Sep 20, 2006)

> Is this basically it?


Yes, you got it. :thumb:


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## Piper (Mar 3, 2011)

chiroken said:


> THANK YOU!!!! The Niagara Falls analogy did it.
> 
> How much you can pump into your tank is limited by how much your drains drain. Pump volume, gph, will be limited to the maximum amnt of water that can drain away. If you pump more than you drain, exceeding your drain capacity, you overflow your tank. As long as your sump resevoir volume is = or > the volume in your tank measuring from highest water point to the siphon break, plus plumbing volume, your sump doesn't overflow (power outage)
> 
> ...


That's about it. I will add one point of clarification. In a power outage situation the volume of water in your tank above not only your siphon overflow but also your return line come into play. In other words, if you stick your return line deep into your tank all the water volume above that nozzle could be siphoned out in reverse back to the pump. To deal with this it is common to place your return nozzle or pipe high in the water column. Some people will also punch or drill small holes in the return line close to the top of the tank where the return line enters the tank. These holes will act to break the siphon in the event of a reverse siphon effect if you lose power.

Jim


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## prov356 (Sep 20, 2006)

> from highest water point to the siphon break


I think he said that, siphon break.


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## chiroken (Sep 25, 2007)

Piper said:


> That's about it. I will add one point of clarification. In a power outage situation the volume of water in your tank above not only your siphon overflow but also your return line come into play. In other words, if you stick your return line deep into your tank all the water volume above that nozzle could be siphoned out in reverse back to the pump. To deal with this it is common to place your return nozzle or pipe high in the water column. Some people will also punch or drill small holes in the return line close to the top of the tank where the return line enters the tank. These holes will act to break the siphon in the event of a reverse siphon effect if you lose power.
> 
> Jim


Yes, the tank will drain to the bottom most point of the overflow if the return line nozzle sits above this point or to the siphon break in the return line, if it is the lowest point.

Thanks everyone, seems pretty simple now but man....just couldn't get me head around it. Also knowing now the average volume of water to drain through a 1" or 1 1/2" drain (600/750 gph)makes it easier as well.

Now the challenge will be to find (used) a narrow enough tank that is long enough to provide the volume I want as I could very well end up with a tank 18 inches deep, not allowing an 18 inch deep sump.


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## cantrell00 (Oct 30, 2010)

A 40 breeder would work for either a 90 or 135...


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## fox (Jun 11, 2009)

chiroken said:


> Yes, the tank will drain to the bottom most point of the overflow if the return line nozzle sits above this point or to the siphon break in the return line, if it is the lowest point.


Not true, the display tank will initially drain the the point dictated by the height of the weir unless the weir is not watertight. The overflow chamber will then drain to the height of the plumbing. Then if allowed by your returns the DT will drain to the point of your return or siphon breaks. Keep your siphon breaks at or around the height of the overflow weir or just below operating water level.



chiroken said:


> >snip< the average volume of water to drain through a 1" or 1 1/2" drain (600/750 gph)makes it easier as well.


A 1-1/2" PVC drain will flow a lot more than 750 gph, actually almost twice that under gravity if the initial vertical drop is at least 20". Check the charts out there. :thumb:


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