# drip water change system questions -- overflows



## 54zamboni (Mar 16, 2005)

what i want to do is put together an auto drip system for three tanks, 180gx2/110g, all with sumps. water dripping into the tanks, exiting from the sumps. i can figure out the part of getting the water dripped in, but the water leaving has me nervous. one of the sumps is acrylic so i can just put a bulkhead in. the other two sumps are non-drilled 40longs. i'm figuring approx. 1/2 gallon per hour on the 180s and 1/3gallon on the 110.

*given that low flow rate, my real question is: will an overflow system on the sumps hold its siphon?*

i have overflow boxes laying around i can use, or would it be better to use a smaller diameter diy pvc overflow, given the low flow rate?

all three will be plumbed into a common drain pipe and then directly to a floor drain, so that part is no problem.


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## The Novice (Jan 27, 2011)

If both ends of a siphon remain below the fluid levels, then the siphon will hold, and operate to equalize the water levels in both water bodies. If either end is exposed, the siphon will collapse. You can use a float valve (like in a toilet) to increase input flow it the output level becomes to low.


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## fmueller (Jan 11, 2004)

If you have an overflow box, that would work, as long as there is enough water going through it to make up for evaporation. With my drip water change systems I change about 10% of system volume per day, and my smallest tank is a 75G. With 7.5G of water going through the overflow in 24h, there is no need to worry about evaporation visibly lowering the water levels, let alone breaking the siphon.

Since I didn't have an overflow box available, I built one from 3/4" PVC pipe. For details see this page. Sorry, my web site is in a bit of disrepair right now.









_Siphon-fed overflow made from 3/4Ã¢â‚¬Â³ PVC pipe Ã¢â‚¬â€œ stretched out on the left, and folded up for easier installation on the right._


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## 54zamboni (Mar 16, 2005)

thanks -- your site has given me a lot of good info. not sure i'm completely getting the evaporation effect -- the water dripping into the tank overflows into the sump -- evaportaion will normally lower the level in the sump, but once the drip system is added, that additional water will make up for the evaporation and the sump should stay pretty much constant at the level of the overflow? it would only be a problem if the evaporation rate is greater than the volume coming in thru the drip system, in which case the sump level would drop . . . . . so if i have 8-12 gallons entering the system each day, even if the evaporation rate was a gallon/day my water level in the sump should always be constant -- sorry, but like i said i'm having trouble grasping the concept . . . .

putting it another way, if the evaporation rate was 1 gallon/day and i'm adding 12 gallons/day, there would be 11 gallons going out thru the overflow in the sump and the water level in the sump would remain constant?


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## jchild40 (Mar 20, 2010)

54zamboni said:


> *given that low flow rate, my real question is: will an overflow system on the sumps hold its siphon?*


So... you're using this overflow/siphon to remove the "old" water displaced by the fresh water and your question is, since the flow is so slow, will the siphon be lost?

If you set up of the overflow like fmueller did, with the u-bends holding water, no air will get into the siphon.


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## fmueller (Jan 11, 2004)

54zamboni said:


> the water dripping into the tank overflows into the sump -- evaporation will normally lower the level in the sump, but once the drip system is added, that additional water will make up for the evaporation and the sump should stay pretty much constant at the level of the overflow?


Yes, that's exactly how it works.

However, you asked if the siphon in the overflow box might break. You don't need any flow to keep up a siphon effect. Only if the water level on one side falls drastically the siphon will break. The only way I could possibly imagine that happening was if the water in the overflow box evaporated (not the water in the sump or the tank). However, even a very slow drip system will send a lot more more water through an overflow box than could possibly evaporate from it.

To make a long story short, your siphon will be safe :thumb:


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## 54zamboni (Mar 16, 2005)

thanks for the help!!! i was just worried that without a significant flow the overflow tube would end up with an ever growing air bubble, restricting or even cutting off the flow. let the project begin. :dancing:


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## fmueller (Jan 11, 2004)

54zamboni said:


> i was just worried that without a significant flow the overflow tube would end up with an ever growing air bubble, restricting or even cutting off the flow.


Truth be told, in my 3/4" PVC pipe overflow, an air bubble does form, but it's a very slow process. If I remove the bubble twice per year, there is never any danger of the siphon breaking. I consider that a very minor inconvenience compared to weekly water changes :lol:


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## 54zamboni (Mar 16, 2005)

Update -- after getting everything set up and running, i was having trouble with the pvc overflow losing its siphon. i took the plunge, bought a glass cutting bit, and after cutting a practice hole on an old 20g, lowered the water level in the 40l sump, and with my wife supplying the water from a spray bottle, drilled out a beautiful 1" hole for the bulkhead. i still have the overflow box on the other sump, but will drill that out eventually as well. after explaining the whole system to my non-fish loving wife, she almost believes i won't flood the basement anymore! thanks again for the help.


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