Working on my first sump and pvc overflow

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jalepeno

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May 4, 2010
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I did the research and built it exactly like the stickies here. I used 1.25" pvc pipe. It turns out that my fx5 pumps water back into the tank faster than the overflow can siphon it back into the sump. I don't think I have any air in the overflow, because no air comes out of the check valve.

I know it isn't ideal to have an fx5 pumping water back into a tank instead of a dedicated pump. This was mostly experimental.

I suppose I'll take this overflow and put it on my 125 and build a new one out of 1.5" pipe for the 180. Unless anybody has any ideas?
 
That's strange. 1.25" pipe should be capable of handling around 925GPH. The FX-5 is capable of pumping 900GPH, but in the configuration you have, it should be pumping less than that (unless your tank is on the ground). Long story short, a properly-built 1.25" should be fine.

Is the overflow draining any water from the tank? When you say "no air comes out of the check valve", were you trying to suck it out with a syringe or aqualifter? The overflow isn't self-bleeding.
 
I was sucking it out with a syringe. The overflow was most definitely draining water from the tank. The water level rose about 3/4" of an inch above the overflow with everything running, and that is when I have to turn the pump off so my tank doesn't overflow. Perhaps I should lower the intake of the overflow a half an inch or so? The overflow was gushing water out, but I have no way to measure the gallons, so maybe I didn't get all of the air bled out of it?
 
Been here, done this. You don't have enough drop in your siphon. The drop is the distance from the water surface inside the tank to the external (behind the tank) cross over tube that is vented. If you increase the drop of the siphon (lower the external cross over tube) you will increase the flow through your over flow pipe.

You did exactly what I did when I made my first overflow tube. You are close, you just need to do a little re-engineering.

I will also mention that the bottom of the U in the pipe inside the tank needs to be several inches below the cross over tube that I am recommending lowering to maintain the vacuum in the siphon. If the U inside the tank is too close to the cross over tube behind the tank the momentum of the water will suck air into the vacuum portion of the tube during a power outage and prevent the overflow from automatically restarting.

My overflow pipe is only 1" and it will easily outflow an FX5... after I modified to increase the drop of the siphon as detailed above.
 
Odd, I followed the design in the sticky exactly. I have the two loops identical, and the whole overflow is 24" tall or so. My tee is about 6" above the bottom of the "U"s.
 
How far is the T below the surface of the water in the tank?

I only have a single overflow pipe (One loop instead of two). My crossover tube (Your T or probably +) is about 6" below the water level in my tank. The U in the bottom of the pipe inside my tank sits on the bottom of my 30" tall tank.

The 6" you have on your internal U should be plenty to maintain the siphon... the T (+) just needs to be lowered with respect to the water level in the tank. I mentioned the internal U because you may have to lower it when you lower your cross over tube... just depends on how much the cross over tube has to be lowered to get the flow you want.

I had the exact problem you are having when I first built my single overflow pipe. Lowering the cross over pipe fixed my problem. I could very well be wrong but I think you have the same problem.

P.S. I followed the same directions you did. :)
 
The center of the tee is exactly 16" from the surface of the water. This is sorta gonna suck taking it apart, as I have already glued it all and I'll have to try and cut it to get it off the tank :-(

I appreciate the help Oughtsix.

Edit: I haven't worked on overflows before. If not all the air was pulled out of it, but enough to keep it running, would it only flow, for example, half as much as it would be capable of?
 
When I built mine I press fit everything together for testing. When I built mine I ended up with 20 gallons of water on the floor when it fell apart through :irked:

Can you post a picture? I would hate to have you take it apart if I am steering you in the wrong direction... it really sounds like the same problem I had though.

What I am calling the crossover pipe is where the water changes direction from going up to going down behind the tank. I just wanted to make sure you understand the part I am talking about. Where the water changes direction from flowing up to flowing down is vented and the venting breaks the siphon. So the total siphon drop is from the tank water level to this external venting point. The closer this point is to the tank water level the slower the system will flow. When this point is at the same level as the tank water there will be no flow at all.
 
these statements that ought is saying are true. i remade mine for my 120 using 1" pvc and i can 900gph no problem at all. when you drop that outside crossover it makes a huge diffrence
 
I cannot get a good picture because of where my tank is and having the background painted. I can find a picture of one designed exactly the same however. It is from the sticky: http://img.photobucket.com/albums/v217/joeytoe/overflow.jpg

The only difference is my pvc is 1.25" and my "C" or vent pipe extends higher than the overflow by about four inches. Mine isn't capped, it is just an open pipe. Is that where I am going wrong?
 
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